diff --git a/config.c b/config.c
index fac7dc3d..bdffd6bb 100644
--- a/config.c
+++ b/config.c
@@ -15,7 +15,7 @@
 #define HOST_BOX_TITLE "Host Name (or IP address)"
 #define PORT_BOX_TITLE "Port"
 
-void conf_radiobutton_handler(union control *ctrl, void *dlg,
+void conf_radiobutton_handler(union control *ctrl, dlgparam *dlg,
 			      void *data, int event)
 {
     int button;
@@ -44,7 +44,7 @@ void conf_radiobutton_handler(union control *ctrl, void *dlg,
 }
 
 #define CHECKBOX_INVERT (1<<30)
-void conf_checkbox_handler(union control *ctrl, void *dlg,
+void conf_checkbox_handler(union control *ctrl, dlgparam *dlg,
 			   void *data, int event)
 {
     int key, invert;
@@ -75,7 +75,7 @@ void conf_checkbox_handler(union control *ctrl, void *dlg,
     }
 }
 
-void conf_editbox_handler(union control *ctrl, void *dlg,
+void conf_editbox_handler(union control *ctrl, dlgparam *dlg,
 			  void *data, int event)
 {
     /*
@@ -124,7 +124,7 @@ void conf_editbox_handler(union control *ctrl, void *dlg,
     }
 }
 
-void conf_filesel_handler(union control *ctrl, void *dlg,
+void conf_filesel_handler(union control *ctrl, dlgparam *dlg,
 			  void *data, int event)
 {
     int key = ctrl->fileselect.context.i;
@@ -139,7 +139,7 @@ void conf_filesel_handler(union control *ctrl, void *dlg,
     }
 }
 
-void conf_fontsel_handler(union control *ctrl, void *dlg,
+void conf_fontsel_handler(union control *ctrl, dlgparam *dlg,
 			  void *data, int event)
 {
     int key = ctrl->fontselect.context.i;
@@ -154,7 +154,7 @@ void conf_fontsel_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void config_host_handler(union control *ctrl, void *dlg,
+static void config_host_handler(union control *ctrl, dlgparam *dlg,
 				void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -186,7 +186,7 @@ static void config_host_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void config_port_handler(union control *ctrl, void *dlg,
+static void config_port_handler(union control *ctrl, dlgparam *dlg,
 				void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -235,7 +235,7 @@ struct hostport {
  * routines can use it to conveniently identify the protocol radio
  * buttons in order to add to them.
  */
-void config_protocolbuttons_handler(union control *ctrl, void *dlg,
+void config_protocolbuttons_handler(union control *ctrl, dlgparam *dlg,
 				    void *data, int event)
 {
     int button;
@@ -289,7 +289,7 @@ void config_protocolbuttons_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void loggingbuttons_handler(union control *ctrl, void *dlg,
+static void loggingbuttons_handler(union control *ctrl, dlgparam *dlg,
 				   void *data, int event)
 {
     int button;
@@ -318,7 +318,7 @@ static void loggingbuttons_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void numeric_keypad_handler(union control *ctrl, void *dlg,
+static void numeric_keypad_handler(union control *ctrl, dlgparam *dlg,
 				   void *data, int event)
 {
     int button;
@@ -349,7 +349,7 @@ static void numeric_keypad_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void cipherlist_handler(union control *ctrl, void *dlg,
+static void cipherlist_handler(union control *ctrl, dlgparam *dlg,
 			       void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -395,7 +395,7 @@ static void cipherlist_handler(union control *ctrl, void *dlg,
 }
 
 #ifndef NO_GSSAPI
-static void gsslist_handler(union control *ctrl, void *dlg,
+static void gsslist_handler(union control *ctrl, dlgparam *dlg,
 			    void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -422,7 +422,7 @@ static void gsslist_handler(union control *ctrl, void *dlg,
 }
 #endif
 
-static void kexlist_handler(union control *ctrl, void *dlg,
+static void kexlist_handler(union control *ctrl, dlgparam *dlg,
 			    void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -466,7 +466,7 @@ static void kexlist_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void hklist_handler(union control *ctrl, void *dlg,
+static void hklist_handler(union control *ctrl, dlgparam *dlg,
                             void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -509,7 +509,7 @@ static void hklist_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void printerbox_handler(union control *ctrl, void *dlg,
+static void printerbox_handler(union control *ctrl, dlgparam *dlg,
 			       void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -545,7 +545,7 @@ static void printerbox_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void codepage_handler(union control *ctrl, void *dlg,
+static void codepage_handler(union control *ctrl, dlgparam *dlg,
 			     void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -569,7 +569,7 @@ static void codepage_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void sshbug_handler(union control *ctrl, void *dlg,
+static void sshbug_handler(union control *ctrl, dlgparam *dlg,
 			   void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -624,7 +624,7 @@ static void sessionsaver_data_free(void *ssdv)
  * failure.
  */
 static int load_selected_session(struct sessionsaver_data *ssd,
-				 void *dlg, Conf *conf, int *maybe_launch)
+                                 dlgparam *dlg, Conf *conf, int *maybe_launch)
 {
     int i = dlg_listbox_index(ssd->listbox, dlg);
     int isdef;
@@ -645,7 +645,7 @@ static int load_selected_session(struct sessionsaver_data *ssd,
     return 1;
 }
 
-static void sessionsaver_handler(union control *ctrl, void *dlg,
+static void sessionsaver_handler(union control *ctrl, dlgparam *dlg,
 				 void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -786,7 +786,7 @@ struct charclass_data {
     union control *listbox, *editbox, *button;
 };
 
-static void charclass_handler(union control *ctrl, void *dlg,
+static void charclass_handler(union control *ctrl, dlgparam *dlg,
 			      void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -841,7 +841,7 @@ static const char *const colours[] = {
     "ANSI White", "ANSI White Bold"
 };
 
-static void colour_handler(union control *ctrl, void *dlg,
+static void colour_handler(union control *ctrl, dlgparam *dlg,
 			    void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -949,7 +949,7 @@ struct ttymodes_data {
     union control *valradio, *valbox, *setbutton, *listbox;
 };
 
-static void ttymodes_handler(union control *ctrl, void *dlg,
+static void ttymodes_handler(union control *ctrl, dlgparam *dlg,
 			     void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -1034,7 +1034,7 @@ struct environ_data {
     union control *varbox, *valbox, *addbutton, *rembutton, *listbox;
 };
 
-static void environ_handler(union control *ctrl, void *dlg,
+static void environ_handler(union control *ctrl, dlgparam *dlg,
 			    void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -1110,7 +1110,7 @@ struct portfwd_data {
 #endif
 };
 
-static void portfwd_handler(union control *ctrl, void *dlg,
+static void portfwd_handler(union control *ctrl, dlgparam *dlg,
 			    void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -1274,7 +1274,7 @@ struct manual_hostkey_data {
     union control *addbutton, *rembutton, *listbox, *keybox;
 };
 
-static void manual_hostkey_handler(union control *ctrl, void *dlg,
+static void manual_hostkey_handler(union control *ctrl, dlgparam *dlg,
                                    void *data, int event)
 {
     Conf *conf = (Conf *)data;
@@ -1337,7 +1337,7 @@ static void manual_hostkey_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void clipboard_selector_handler(union control *ctrl, void *dlg,
+static void clipboard_selector_handler(union control *ctrl, dlgparam *dlg,
                                        void *data, int event)
 {
     Conf *conf = (Conf *)data;
diff --git a/defs.h b/defs.h
index 329883d9..1bc8f9b8 100644
--- a/defs.h
+++ b/defs.h
@@ -59,6 +59,8 @@ typedef struct ssh_sharing_state ssh_sharing_state;
 typedef struct ssh_sharing_connstate ssh_sharing_connstate;
 typedef struct share_channel share_channel;
 
+typedef struct dlgparam dlgparam;
+
 /* Note indirection: for historical reasons (it used to be closer to
  * the OS socket type), the type that most code uses for a socket is
  * 'Socket', not 'Socket *'. So an implementation of Socket or Plug
diff --git a/dialog.h b/dialog.h
index 68f7dff1..4b708489 100644
--- a/dialog.h
+++ b/dialog.h
@@ -103,7 +103,7 @@ enum {
     EVENT_SELCHANGE,
     EVENT_CALLBACK
 };
-typedef void (*handler_fn)(union control *ctrl, void *dlg,
+typedef void (*handler_fn)(union control *ctrl, dlgparam *dp,
 			   void *data, int event);
 
 #define STANDARD_PREFIX \
@@ -534,16 +534,16 @@ union control *ctrl_tabdelay(struct controlset *, union control *);
  * Routines the platform-independent dialog code can call to read
  * and write the values of controls.
  */
-void dlg_radiobutton_set(union control *ctrl, void *dlg, int whichbutton);
-int dlg_radiobutton_get(union control *ctrl, void *dlg);
-void dlg_checkbox_set(union control *ctrl, void *dlg, int checked);
-int dlg_checkbox_get(union control *ctrl, void *dlg);
-void dlg_editbox_set(union control *ctrl, void *dlg, char const *text);
-char *dlg_editbox_get(union control *ctrl, void *dlg);   /* result must be freed by caller */
+void dlg_radiobutton_set(union control *ctrl, dlgparam *dp, int whichbutton);
+int dlg_radiobutton_get(union control *ctrl, dlgparam *dp);
+void dlg_checkbox_set(union control *ctrl, dlgparam *dp, int checked);
+int dlg_checkbox_get(union control *ctrl, dlgparam *dp);
+void dlg_editbox_set(union control *ctrl, dlgparam *dp, char const *text);
+char *dlg_editbox_get(union control *ctrl, dlgparam *dp);   /* result must be freed by caller */
 /* The `listbox' functions can also apply to combo boxes. */
-void dlg_listbox_clear(union control *ctrl, void *dlg);
-void dlg_listbox_del(union control *ctrl, void *dlg, int index);
-void dlg_listbox_add(union control *ctrl, void *dlg, char const *text);
+void dlg_listbox_clear(union control *ctrl, dlgparam *dp);
+void dlg_listbox_del(union control *ctrl, dlgparam *dp, int index);
+void dlg_listbox_add(union control *ctrl, dlgparam *dp, char const *text);
 /*
  * Each listbox entry may have a numeric id associated with it.
  * Note that some front ends only permit a string to be stored at
@@ -551,53 +551,53 @@ void dlg_listbox_add(union control *ctrl, void *dlg, char const *text);
  * strings in any listbox then you MUST not assign them different
  * IDs and expect to get meaningful results back.
  */
-void dlg_listbox_addwithid(union control *ctrl, void *dlg,
+void dlg_listbox_addwithid(union control *ctrl, dlgparam *dp,
 			   char const *text, int id);
-int dlg_listbox_getid(union control *ctrl, void *dlg, int index);
+int dlg_listbox_getid(union control *ctrl, dlgparam *dp, int index);
 /* dlg_listbox_index returns <0 if no single element is selected. */
-int dlg_listbox_index(union control *ctrl, void *dlg);
-int dlg_listbox_issel(union control *ctrl, void *dlg, int index);
-void dlg_listbox_select(union control *ctrl, void *dlg, int index);
-void dlg_text_set(union control *ctrl, void *dlg, char const *text);
-void dlg_filesel_set(union control *ctrl, void *dlg, Filename *fn);
-Filename *dlg_filesel_get(union control *ctrl, void *dlg);
-void dlg_fontsel_set(union control *ctrl, void *dlg, FontSpec *fn);
-FontSpec *dlg_fontsel_get(union control *ctrl, void *dlg);
+int dlg_listbox_index(union control *ctrl, dlgparam *dp);
+int dlg_listbox_issel(union control *ctrl, dlgparam *dp, int index);
+void dlg_listbox_select(union control *ctrl, dlgparam *dp, int index);
+void dlg_text_set(union control *ctrl, dlgparam *dp, char const *text);
+void dlg_filesel_set(union control *ctrl, dlgparam *dp, Filename *fn);
+Filename *dlg_filesel_get(union control *ctrl, dlgparam *dp);
+void dlg_fontsel_set(union control *ctrl, dlgparam *dp, FontSpec *fn);
+FontSpec *dlg_fontsel_get(union control *ctrl, dlgparam *dp);
 /*
  * Bracketing a large set of updates in these two functions will
  * cause the front end (if possible) to delay updating the screen
  * until it's all complete, thus avoiding flicker.
  */
-void dlg_update_start(union control *ctrl, void *dlg);
-void dlg_update_done(union control *ctrl, void *dlg);
+void dlg_update_start(union control *ctrl, dlgparam *dp);
+void dlg_update_done(union control *ctrl, dlgparam *dp);
 /*
  * Set input focus into a particular control.
  */
-void dlg_set_focus(union control *ctrl, void *dlg);
+void dlg_set_focus(union control *ctrl, dlgparam *dp);
 /*
  * Change the label text on a control.
  */
-void dlg_label_change(union control *ctrl, void *dlg, char const *text);
+void dlg_label_change(union control *ctrl, dlgparam *dp, char const *text);
 /*
  * Return the `ctrl' structure for the most recent control that had
  * the input focus apart from the one mentioned. This is NOT
  * GUARANTEED to work on all platforms, so don't base any critical
  * functionality on it!
  */
-union control *dlg_last_focused(union control *ctrl, void *dlg);
+union control *dlg_last_focused(union control *ctrl, dlgparam *dp);
 /*
  * During event processing, you might well want to give an error
  * indication to the user. dlg_beep() is a quick and easy generic
  * error; dlg_error() puts up a message-box or equivalent.
  */
-void dlg_beep(void *dlg);
-void dlg_error_msg(void *dlg, const char *msg);
+void dlg_beep(dlgparam *dp);
+void dlg_error_msg(dlgparam *dp, const char *msg);
 /*
  * This function signals to the front end that the dialog's
  * processing is completed, and passes an integer value (typically
  * a success status).
  */
-void dlg_end(void *dlg, int value);
+void dlg_end(dlgparam *dp, int value);
 
 /*
  * Routines to manage a (per-platform) colour selector.
@@ -612,9 +612,9 @@ void dlg_end(void *dlg, int value);
  * dlg_coloursel_start() accepts an RGB triple which is used to
  * initialise the colour selector to its starting value.
  */
-void dlg_coloursel_start(union control *ctrl, void *dlg,
+void dlg_coloursel_start(union control *ctrl, dlgparam *dp,
 			 int r, int g, int b);
-int dlg_coloursel_results(union control *ctrl, void *dlg,
+int dlg_coloursel_results(union control *ctrl, dlgparam *dp,
 			  int *r, int *g, int *b);
 
 /*
@@ -626,7 +626,7 @@ int dlg_coloursel_results(union control *ctrl, void *dlg,
  * If `ctrl' is NULL, _all_ controls in the dialog get refreshed
  * (for loading or saving entire sets of settings).
  */
-void dlg_refresh(union control *ctrl, void *dlg);
+void dlg_refresh(union control *ctrl, dlgparam *dp);
 
 /*
  * Standard helper functions for reading a controlbox structure.
diff --git a/putty.h b/putty.h
index 1a8c30ce..7b1f90e4 100644
--- a/putty.h
+++ b/putty.h
@@ -1421,16 +1421,16 @@ void cmdline_error(const char *, ...);
  */
 struct controlbox;
 union control;
-void conf_radiobutton_handler(union control *ctrl, void *dlg,
+void conf_radiobutton_handler(union control *ctrl, dlgparam *dlg,
 			      void *data, int event);
 #define CHECKBOX_INVERT (1<<30)
-void conf_checkbox_handler(union control *ctrl, void *dlg,
+void conf_checkbox_handler(union control *ctrl, dlgparam *dlg,
 			   void *data, int event);
-void conf_editbox_handler(union control *ctrl, void *dlg,
+void conf_editbox_handler(union control *ctrl, dlgparam *dlg,
 			  void *data, int event);
-void conf_filesel_handler(union control *ctrl, void *dlg,
+void conf_filesel_handler(union control *ctrl, dlgparam *dlg,
 			  void *data, int event);
-void conf_fontsel_handler(union control *ctrl, void *dlg,
+void conf_fontsel_handler(union control *ctrl, dlgparam *dlg,
 			  void *data, int event);
 void setup_config_box(struct controlbox *b, int midsession,
 		      int protocol, int protcfginfo);
diff --git a/sercfg.c b/sercfg.c
index fef910f3..71462100 100644
--- a/sercfg.c
+++ b/sercfg.c
@@ -16,7 +16,7 @@
 #include "dialog.h"
 #include "storage.h"
 
-static void serial_parity_handler(union control *ctrl, void *dlg,
+static void serial_parity_handler(union control *ctrl, dlgparam *dlg,
 				  void *data, int event)
 {
     static const struct {
@@ -71,7 +71,7 @@ static void serial_parity_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void serial_flow_handler(union control *ctrl, void *dlg,
+static void serial_flow_handler(union control *ctrl, dlgparam *dlg,
 				void *data, int event)
 {
     static const struct {
@@ -132,7 +132,7 @@ void ser_setup_config_box(struct controlbox *b, int midsession,
 
     if (!midsession) {
 	int i;
-	extern void config_protocolbuttons_handler(union control *, void *,
+        extern void config_protocolbuttons_handler(union control *, dlgparam *,
 						   void *, int);
 
 	/*
diff --git a/unix/gtkcfg.c b/unix/gtkcfg.c
index 4307176f..bbde8d2a 100644
--- a/unix/gtkcfg.c
+++ b/unix/gtkcfg.c
@@ -10,7 +10,7 @@
 #include "dialog.h"
 #include "storage.h"
 
-static void about_handler(union control *ctrl, void *dlg,
+static void about_handler(union control *ctrl, dlgparam *dlg,
 			  void *data, int event)
 {
     if (event == EVENT_ACTION) {
diff --git a/unix/gtkdlg.c b/unix/gtkdlg.c
index f1425daf..6ffb5b5c 100644
--- a/unix/gtkdlg.c
+++ b/unix/gtkdlg.c
@@ -252,27 +252,24 @@ static struct uctrl *dlg_find_bywidget(struct dlgparam *dp, GtkWidget *w)
     return ret;
 }
 
-union control *dlg_last_focused(union control *ctrl, void *dlg)
+union control *dlg_last_focused(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     if (dp->currfocus != ctrl)
         return dp->currfocus;
     else
         return dp->lastfocus;
 }
 
-void dlg_radiobutton_set(union control *ctrl, void *dlg, int which)
+void dlg_radiobutton_set(union control *ctrl, dlgparam *dp, int which)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
     assert(uc->ctrl->generic.type == CTRL_RADIO);
     assert(uc->buttons != NULL);
     gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(uc->buttons[which]), TRUE);
 }
 
-int dlg_radiobutton_get(union control *ctrl, void *dlg)
+int dlg_radiobutton_get(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
     int i;
 
@@ -284,25 +281,22 @@ int dlg_radiobutton_get(union control *ctrl, void *dlg)
     return 0;			       /* got to return something */
 }
 
-void dlg_checkbox_set(union control *ctrl, void *dlg, int checked)
+void dlg_checkbox_set(union control *ctrl, dlgparam *dp, int checked)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
     assert(uc->ctrl->generic.type == CTRL_CHECKBOX);
     gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(uc->toplevel), checked);
 }
 
-int dlg_checkbox_get(union control *ctrl, void *dlg)
+int dlg_checkbox_get(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
     assert(uc->ctrl->generic.type == CTRL_CHECKBOX);
     return gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(uc->toplevel));
 }
 
-void dlg_editbox_set(union control *ctrl, void *dlg, char const *text)
+void dlg_editbox_set(union control *ctrl, dlgparam *dp, char const *text)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
     GtkWidget *entry;
     char *tmpstring;
@@ -339,9 +333,8 @@ void dlg_editbox_set(union control *ctrl, void *dlg, char const *text)
     sfree(tmpstring);
 }
 
-char *dlg_editbox_get(union control *ctrl, void *dlg)
+char *dlg_editbox_get(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
     assert(uc->ctrl->generic.type == CTRL_EDITBOX);
 
@@ -369,9 +362,8 @@ static void container_remove_and_destroy(GtkWidget *w, gpointer data)
 #endif
 
 /* The `listbox' functions can also apply to combo boxes. */
-void dlg_listbox_clear(union control *ctrl, void *dlg)
+void dlg_listbox_clear(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
 
     assert(uc->ctrl->generic.type == CTRL_EDITBOX ||
@@ -398,9 +390,8 @@ void dlg_listbox_clear(union control *ctrl, void *dlg)
     assert(!"We shouldn't get here");
 }
 
-void dlg_listbox_del(union control *ctrl, void *dlg, int index)
+void dlg_listbox_del(union control *ctrl, dlgparam *dp, int index)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
 
     assert(uc->ctrl->generic.type == CTRL_EDITBOX ||
@@ -433,9 +424,9 @@ void dlg_listbox_del(union control *ctrl, void *dlg, int index)
     assert(!"We shouldn't get here");
 }
 
-void dlg_listbox_add(union control *ctrl, void *dlg, char const *text)
+void dlg_listbox_add(union control *ctrl, dlgparam *dp, char const *text)
 {
-    dlg_listbox_addwithid(ctrl, dlg, text, 0);
+    dlg_listbox_addwithid(ctrl, dp, text, 0);
 }
 
 /*
@@ -445,10 +436,9 @@ void dlg_listbox_add(union control *ctrl, void *dlg, char const *text)
  * strings in any listbox then you MUST not assign them different
  * IDs and expect to get meaningful results back.
  */
-void dlg_listbox_addwithid(union control *ctrl, void *dlg,
+void dlg_listbox_addwithid(union control *ctrl, dlgparam *dp,
 			   char const *text, int id)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
 
     assert(uc->ctrl->generic.type == CTRL_EDITBOX ||
@@ -594,9 +584,8 @@ void dlg_listbox_addwithid(union control *ctrl, void *dlg,
     dp->flags &= ~FLAG_UPDATING_COMBO_LIST;
 }
 
-int dlg_listbox_getid(union control *ctrl, void *dlg, int index)
+int dlg_listbox_getid(union control *ctrl, dlgparam *dp, int index)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
 
     assert(uc->ctrl->generic.type == CTRL_EDITBOX ||
@@ -634,9 +623,8 @@ int dlg_listbox_getid(union control *ctrl, void *dlg, int index)
 }
 
 /* dlg_listbox_index returns <0 if no single element is selected. */
-int dlg_listbox_index(union control *ctrl, void *dlg)
+int dlg_listbox_index(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
 
     assert(uc->ctrl->generic.type == CTRL_EDITBOX ||
@@ -719,9 +707,8 @@ int dlg_listbox_index(union control *ctrl, void *dlg)
     return -1;			       /* placate dataflow analysis */
 }
 
-int dlg_listbox_issel(union control *ctrl, void *dlg, int index)
+int dlg_listbox_issel(union control *ctrl, dlgparam *dp, int index)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
 
     assert(uc->ctrl->generic.type == CTRL_EDITBOX ||
@@ -777,9 +764,8 @@ int dlg_listbox_issel(union control *ctrl, void *dlg, int index)
     return -1;			       /* placate dataflow analysis */
 }
 
-void dlg_listbox_select(union control *ctrl, void *dlg, int index)
+void dlg_listbox_select(union control *ctrl, dlgparam *dp, int index)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
 
     assert(uc->ctrl->generic.type == CTRL_EDITBOX ||
@@ -846,9 +832,8 @@ void dlg_listbox_select(union control *ctrl, void *dlg, int index)
     assert(!"We shouldn't get here");
 }
 
-void dlg_text_set(union control *ctrl, void *dlg, char const *text)
+void dlg_text_set(union control *ctrl, dlgparam *dp, char const *text)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
 
     assert(uc->ctrl->generic.type == CTRL_TEXT);
@@ -857,9 +842,8 @@ void dlg_text_set(union control *ctrl, void *dlg, char const *text)
     gtk_label_set_text(GTK_LABEL(uc->text), text);
 }
 
-void dlg_label_change(union control *ctrl, void *dlg, char const *text)
+void dlg_label_change(union control *ctrl, dlgparam *dp, char const *text)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
 
     switch (uc->ctrl->generic.type) {
@@ -897,9 +881,8 @@ void dlg_label_change(union control *ctrl, void *dlg, char const *text)
     }
 }
 
-void dlg_filesel_set(union control *ctrl, void *dlg, Filename *fn)
+void dlg_filesel_set(union control *ctrl, dlgparam *dp, Filename *fn)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
     /* We must copy fn->path before passing it to gtk_entry_set_text.
      * See comment in dlg_editbox_set() for the reasons. */
@@ -910,18 +893,16 @@ void dlg_filesel_set(union control *ctrl, void *dlg, Filename *fn)
     sfree(duppath);
 }
 
-Filename *dlg_filesel_get(union control *ctrl, void *dlg)
+Filename *dlg_filesel_get(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
     assert(uc->ctrl->generic.type == CTRL_FILESELECT);
     assert(uc->entry != NULL);
     return filename_from_str(gtk_entry_get_text(GTK_ENTRY(uc->entry)));
 }
 
-void dlg_fontsel_set(union control *ctrl, void *dlg, FontSpec *fs)
+void dlg_fontsel_set(union control *ctrl, dlgparam *dp, FontSpec *fs)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
     /* We must copy fs->name before passing it to gtk_entry_set_text.
      * See comment in dlg_editbox_set() for the reasons. */
@@ -932,9 +913,8 @@ void dlg_fontsel_set(union control *ctrl, void *dlg, FontSpec *fs)
     sfree(dupname);
 }
 
-FontSpec *dlg_fontsel_get(union control *ctrl, void *dlg)
+FontSpec *dlg_fontsel_get(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
     assert(uc->ctrl->generic.type == CTRL_FONTSELECT);
     assert(uc->entry != NULL);
@@ -946,7 +926,7 @@ FontSpec *dlg_fontsel_get(union control *ctrl, void *dlg)
  * cause the front end (if possible) to delay updating the screen
  * until it's all complete, thus avoiding flicker.
  */
-void dlg_update_start(union control *ctrl, void *dlg)
+void dlg_update_start(union control *ctrl, dlgparam *dp)
 {
     /*
      * Apparently we can't do this at all in GTK. GtkCList supports
@@ -954,7 +934,7 @@ void dlg_update_start(union control *ctrl, void *dlg)
      */
 }
 
-void dlg_update_done(union control *ctrl, void *dlg)
+void dlg_update_done(union control *ctrl, dlgparam *dp)
 {
     /*
      * Apparently we can't do this at all in GTK. GtkCList supports
@@ -962,9 +942,8 @@ void dlg_update_done(union control *ctrl, void *dlg)
      */
 }
 
-void dlg_set_focus(union control *ctrl, void *dlg)
+void dlg_set_focus(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
 
     switch (ctrl->generic.type) {
@@ -1039,7 +1018,7 @@ void dlg_set_focus(union control *ctrl, void *dlg)
  * indication to the user. dlg_beep() is a quick and easy generic
  * error; dlg_error() puts up a message-box or equivalent.
  */
-void dlg_beep(void *dlg)
+void dlg_beep(dlgparam *dp)
 {
     gdk_display_beep(gdk_display_get_default());
 }
@@ -1079,9 +1058,8 @@ void trivial_post_dialog_fn(void *vctx, int result)
 {
 }
 
-void dlg_error_msg(void *dlg, const char *msg)
+void dlg_error_msg(dlgparam *dp, const char *msg)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     create_message_box(
         dp->window, "Error", msg,
         string_width("Some sort of text about a config-box error message"),
@@ -1093,16 +1071,14 @@ void dlg_error_msg(void *dlg, const char *msg)
  * processing is completed, and passes an integer value (typically
  * a success status).
  */
-void dlg_end(void *dlg, int value)
+void dlg_end(dlgparam *dp, int value)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     dp->retval = value;
     gtk_widget_destroy(dp->window);
 }
 
-void dlg_refresh(union control *ctrl, void *dlg)
+void dlg_refresh(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc;
 
     if (ctrl) {
@@ -1120,9 +1096,8 @@ void dlg_refresh(union control *ctrl, void *dlg)
     }
 }
 
-void dlg_coloursel_start(union control *ctrl, void *dlg, int r, int g, int b)
+void dlg_coloursel_start(union control *ctrl, dlgparam *dp, int r, int g, int b)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct uctrl *uc = dlg_find_byctrl(dp, ctrl);
 
 #if GTK_CHECK_VERSION(3,0,0)
@@ -1206,10 +1181,9 @@ void dlg_coloursel_start(union control *ctrl, void *dlg, int r, int g, int b)
     gtk_widget_show(coloursel);
 }
 
-int dlg_coloursel_results(union control *ctrl, void *dlg,
+int dlg_coloursel_results(union control *ctrl, dlgparam *dp,
 			  int *r, int *g, int *b)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     if (dp->coloursel_result.ok) {
 	*r = dp->coloursel_result.r;
 	*g = dp->coloursel_result.g;
@@ -3283,11 +3257,11 @@ static void dlgparam_destroy(GtkWidget *widget, gpointer data)
     sfree(dp);
 }
 
-static void messagebox_handler(union control *ctrl, void *dlg,
+static void messagebox_handler(union control *ctrl, dlgparam *dp,
 			       void *data, int event)
 {
     if (event == EVENT_ACTION)
-	dlg_end(dlg, ctrl->generic.context.i);
+        dlg_end(dp, ctrl->generic.context.i);
 }
 
 const struct message_box_button button_array_yn[] = {
@@ -3806,13 +3780,13 @@ static void eventlog_destroy(GtkWidget *widget, gpointer data)
     dlg_cleanup(&es->dp);
     ctrl_free_box(es->eventbox);
 }
-static void eventlog_ok_handler(union control *ctrl, void *dlg,
+static void eventlog_ok_handler(union control *ctrl, dlgparam *dp,
 				void *data, int event)
 {
     if (event == EVENT_ACTION)
-	dlg_end(dlg, 0);
+        dlg_end(dp, 0);
 }
-static void eventlog_list_handler(union control *ctrl, void *dlg,
+static void eventlog_list_handler(union control *ctrl, dlgparam *dp,
 				  void *data, int event)
 {
     struct eventlog_stuff *es = (struct eventlog_stuff *)data;
@@ -3820,15 +3794,15 @@ static void eventlog_list_handler(union control *ctrl, void *dlg,
     if (event == EVENT_REFRESH) {
 	int i;
 
-	dlg_update_start(ctrl, dlg);
-	dlg_listbox_clear(ctrl, dlg);
+        dlg_update_start(ctrl, dp);
+        dlg_listbox_clear(ctrl, dp);
 	for (i = 0; i < es->ninitial; i++) {
-	    dlg_listbox_add(ctrl, dlg, es->events_initial[i]);
+            dlg_listbox_add(ctrl, dp, es->events_initial[i]);
 	}
 	for (i = 0; i < es->ncircular; i++) {
-	    dlg_listbox_add(ctrl, dlg, es->events_circular[(es->circular_first + i) % LOGEVENT_CIRCULAR_MAX]);
+            dlg_listbox_add(ctrl, dp, es->events_circular[(es->circular_first + i) % LOGEVENT_CIRCULAR_MAX]);
 	}
-	dlg_update_done(ctrl, dlg);
+        dlg_update_done(ctrl, dp);
     } else if (event == EVENT_SELCHANGE) {
         int i;
         int selsize = 0;
@@ -3849,7 +3823,7 @@ static void eventlog_list_handler(union control *ctrl, void *dlg,
         es->seldata = NULL;
         es->sellen = 0;
         for (i = 0; i < es->ninitial; i++) {
-            if (dlg_listbox_issel(ctrl, dlg, i)) {
+            if (dlg_listbox_issel(ctrl, dp, i)) {
                 int extralen = strlen(es->events_initial[i]);
 
                 if (es->sellen + extralen + 2 > selsize) {
@@ -3863,7 +3837,7 @@ static void eventlog_list_handler(union control *ctrl, void *dlg,
             }
         }
         for (i = 0; i < es->ncircular; i++) {
-            if (dlg_listbox_issel(ctrl, dlg, es->ninitial + i)) {
+            if (dlg_listbox_issel(ctrl, dp, es->ninitial + i)) {
                 int j = (es->circular_first + i) % LOGEVENT_CIRCULAR_MAX;
                 int extralen = strlen(es->events_circular[j]);
 
diff --git a/windows/wincfg.c b/windows/wincfg.c
index 9e242875..8131883c 100644
--- a/windows/wincfg.c
+++ b/windows/wincfg.c
@@ -10,7 +10,7 @@
 #include "dialog.h"
 #include "storage.h"
 
-static void about_handler(union control *ctrl, void *dlg,
+static void about_handler(union control *ctrl, dlgparam *dlg,
 			  void *data, int event)
 {
     HWND *hwndp = (HWND *)ctrl->generic.context.p;
@@ -20,7 +20,7 @@ static void about_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void help_handler(union control *ctrl, void *dlg,
+static void help_handler(union control *ctrl, dlgparam *dlg,
 			 void *data, int event)
 {
     HWND *hwndp = (HWND *)ctrl->generic.context.p;
@@ -30,7 +30,7 @@ static void help_handler(union control *ctrl, void *dlg,
     }
 }
 
-static void variable_pitch_handler(union control *ctrl, void *dlg,
+static void variable_pitch_handler(union control *ctrl, dlgparam *dlg,
                                    void *data, int event)
 {
     if (event == EVENT_REFRESH) {
diff --git a/windows/winctrls.c b/windows/winctrls.c
index da2fac62..1b51598f 100644
--- a/windows/winctrls.c
+++ b/windows/winctrls.c
@@ -1722,9 +1722,8 @@ static void winctrl_set_focus(union control *ctrl, struct dlgparam *dp,
     }
 }
 
-union control *dlg_last_focused(union control *ctrl, void *dlg)
+union control *dlg_last_focused(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     return dp->focused == ctrl ? dp->lastfocused : dp->focused;
 }
 
@@ -2067,9 +2066,8 @@ static struct winctrl *dlg_findbyctrl(struct dlgparam *dp, union control *ctrl)
     return NULL;
 }
 
-void dlg_radiobutton_set(union control *ctrl, void *dlg, int whichbutton)
+void dlg_radiobutton_set(union control *ctrl, dlgparam *dp, int whichbutton)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     assert(c && c->ctrl->generic.type == CTRL_RADIO);
     CheckRadioButton(dp->hwnd,
@@ -2078,9 +2076,8 @@ void dlg_radiobutton_set(union control *ctrl, void *dlg, int whichbutton)
 		     c->base_id + 1 + whichbutton);
 }
 
-int dlg_radiobutton_get(union control *ctrl, void *dlg)
+int dlg_radiobutton_get(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     int i;
     assert(c && c->ctrl->generic.type == CTRL_RADIO);
@@ -2091,42 +2088,37 @@ int dlg_radiobutton_get(union control *ctrl, void *dlg)
     return 0;
 }
 
-void dlg_checkbox_set(union control *ctrl, void *dlg, int checked)
+void dlg_checkbox_set(union control *ctrl, dlgparam *dp, int checked)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     assert(c && c->ctrl->generic.type == CTRL_CHECKBOX);
     CheckDlgButton(dp->hwnd, c->base_id, (checked != 0));
 }
 
-int dlg_checkbox_get(union control *ctrl, void *dlg)
+int dlg_checkbox_get(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     assert(c && c->ctrl->generic.type == CTRL_CHECKBOX);
     return 0 != IsDlgButtonChecked(dp->hwnd, c->base_id);
 }
 
-void dlg_editbox_set(union control *ctrl, void *dlg, char const *text)
+void dlg_editbox_set(union control *ctrl, dlgparam *dp, char const *text)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     assert(c && c->ctrl->generic.type == CTRL_EDITBOX);
     SetDlgItemText(dp->hwnd, c->base_id+1, text);
 }
 
-char *dlg_editbox_get(union control *ctrl, void *dlg)
+char *dlg_editbox_get(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     assert(c && c->ctrl->generic.type == CTRL_EDITBOX);
     return GetDlgItemText_alloc(dp->hwnd, c->base_id+1);
 }
 
 /* The `listbox' functions can also apply to combo boxes. */
-void dlg_listbox_clear(union control *ctrl, void *dlg)
+void dlg_listbox_clear(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     int msg;
     assert(c &&
@@ -2138,9 +2130,8 @@ void dlg_listbox_clear(union control *ctrl, void *dlg)
     SendDlgItemMessage(dp->hwnd, c->base_id+1, msg, 0, 0);
 }
 
-void dlg_listbox_del(union control *ctrl, void *dlg, int index)
+void dlg_listbox_del(union control *ctrl, dlgparam *dp, int index)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     int msg;
     assert(c &&
@@ -2152,9 +2143,8 @@ void dlg_listbox_del(union control *ctrl, void *dlg, int index)
     SendDlgItemMessage(dp->hwnd, c->base_id+1, msg, index, 0);
 }
 
-void dlg_listbox_add(union control *ctrl, void *dlg, char const *text)
+void dlg_listbox_add(union control *ctrl, dlgparam *dp, char const *text)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     int msg;
     assert(c &&
@@ -2173,10 +2163,9 @@ void dlg_listbox_add(union control *ctrl, void *dlg, char const *text)
  * strings in any listbox then you MUST not assign them different
  * IDs and expect to get meaningful results back.
  */
-void dlg_listbox_addwithid(union control *ctrl, void *dlg,
+void dlg_listbox_addwithid(union control *ctrl, dlgparam *dp,
 			   char const *text, int id)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     int msg, msg2, index;
     assert(c &&
@@ -2191,9 +2180,8 @@ void dlg_listbox_addwithid(union control *ctrl, void *dlg,
     SendDlgItemMessage(dp->hwnd, c->base_id+1, msg2, index, (LPARAM)id);
 }
 
-int dlg_listbox_getid(union control *ctrl, void *dlg, int index)
+int dlg_listbox_getid(union control *ctrl, dlgparam *dp, int index)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     int msg;
     assert(c && c->ctrl->generic.type == CTRL_LISTBOX);
@@ -2203,9 +2191,8 @@ int dlg_listbox_getid(union control *ctrl, void *dlg, int index)
 }
 
 /* dlg_listbox_index returns <0 if no single element is selected. */
-int dlg_listbox_index(union control *ctrl, void *dlg)
+int dlg_listbox_index(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     int msg, ret;
     assert(c && c->ctrl->generic.type == CTRL_LISTBOX);
@@ -2223,9 +2210,8 @@ int dlg_listbox_index(union control *ctrl, void *dlg)
 	return ret;
 }
 
-int dlg_listbox_issel(union control *ctrl, void *dlg, int index)
+int dlg_listbox_issel(union control *ctrl, dlgparam *dp, int index)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     assert(c && c->ctrl->generic.type == CTRL_LISTBOX &&
 	   c->ctrl->listbox.multisel &&
@@ -2234,9 +2220,8 @@ int dlg_listbox_issel(union control *ctrl, void *dlg, int index)
 	SendDlgItemMessage(dp->hwnd, c->base_id+1, LB_GETSEL, index, 0);
 }
 
-void dlg_listbox_select(union control *ctrl, void *dlg, int index)
+void dlg_listbox_select(union control *ctrl, dlgparam *dp, int index)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     int msg;
     assert(c && c->ctrl->generic.type == CTRL_LISTBOX &&
@@ -2245,17 +2230,15 @@ void dlg_listbox_select(union control *ctrl, void *dlg, int index)
     SendDlgItemMessage(dp->hwnd, c->base_id+1, msg, index, 0);
 }
 
-void dlg_text_set(union control *ctrl, void *dlg, char const *text)
+void dlg_text_set(union control *ctrl, dlgparam *dp, char const *text)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     assert(c && c->ctrl->generic.type == CTRL_TEXT);
     SetDlgItemText(dp->hwnd, c->base_id, text);
 }
 
-void dlg_label_change(union control *ctrl, void *dlg, char const *text)
+void dlg_label_change(union control *ctrl, dlgparam *dp, char const *text)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     char *escaped = NULL;
     int id = -1;
@@ -2300,17 +2283,15 @@ void dlg_label_change(union control *ctrl, void *dlg, char const *text)
     }
 }
 
-void dlg_filesel_set(union control *ctrl, void *dlg, Filename *fn)
+void dlg_filesel_set(union control *ctrl, dlgparam *dp, Filename *fn)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     assert(c && c->ctrl->generic.type == CTRL_FILESELECT);
     SetDlgItemText(dp->hwnd, c->base_id+1, fn->path);
 }
 
-Filename *dlg_filesel_get(union control *ctrl, void *dlg)
+Filename *dlg_filesel_get(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     char *tmp;
     Filename *ret;
@@ -2321,10 +2302,9 @@ Filename *dlg_filesel_get(union control *ctrl, void *dlg)
     return ret;
 }
 
-void dlg_fontsel_set(union control *ctrl, void *dlg, FontSpec *fs)
+void dlg_fontsel_set(union control *ctrl, dlgparam *dp, FontSpec *fs)
 {
     char *buf, *boldstr;
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     assert(c && c->ctrl->generic.type == CTRL_FONTSELECT);
 
@@ -2344,9 +2324,8 @@ void dlg_fontsel_set(union control *ctrl, void *dlg, FontSpec *fs)
     dlg_auto_set_fixed_pitch_flag(dp);
 }
 
-FontSpec *dlg_fontsel_get(union control *ctrl, void *dlg)
+FontSpec *dlg_fontsel_get(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     assert(c && c->ctrl->generic.type == CTRL_FONTSELECT);
     return fontspec_copy((FontSpec *)c->data);
@@ -2357,18 +2336,16 @@ FontSpec *dlg_fontsel_get(union control *ctrl, void *dlg)
  * cause the front end (if possible) to delay updating the screen
  * until it's all complete, thus avoiding flicker.
  */
-void dlg_update_start(union control *ctrl, void *dlg)
+void dlg_update_start(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     if (c && c->ctrl->generic.type == CTRL_LISTBOX) {
 	SendDlgItemMessage(dp->hwnd, c->base_id+1, WM_SETREDRAW, FALSE, 0);
     }
 }
 
-void dlg_update_done(union control *ctrl, void *dlg)
+void dlg_update_done(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     if (c && c->ctrl->generic.type == CTRL_LISTBOX) {
 	HWND hw = GetDlgItem(dp->hwnd, c->base_id+1);
@@ -2377,9 +2354,8 @@ void dlg_update_done(union control *ctrl, void *dlg)
     }
 }
 
-void dlg_set_focus(union control *ctrl, void *dlg)
+void dlg_set_focus(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     struct winctrl *c = dlg_findbyctrl(dp, ctrl);
     int id;
     HWND ctl;
@@ -2413,15 +2389,13 @@ void dlg_set_focus(union control *ctrl, void *dlg)
  * indication to the user. dlg_beep() is a quick and easy generic
  * error; dlg_error() puts up a message-box or equivalent.
  */
-void dlg_beep(void *dlg)
+void dlg_beep(dlgparam *dp)
 {
-    /* struct dlgparam *dp = (struct dlgparam *)dlg; */
     MessageBeep(0);
 }
 
-void dlg_error_msg(void *dlg, const char *msg)
+void dlg_error_msg(dlgparam *dp, const char *msg)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     MessageBox(dp->hwnd, msg,
 	       dp->errtitle ? dp->errtitle : NULL,
 	       MB_OK | MB_ICONERROR);
@@ -2432,16 +2406,14 @@ void dlg_error_msg(void *dlg, const char *msg)
  * processing is completed, and passes an integer value (typically
  * a success status).
  */
-void dlg_end(void *dlg, int value)
+void dlg_end(dlgparam *dp, int value)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     dp->ended = TRUE;
     dp->endresult = value;
 }
 
-void dlg_refresh(union control *ctrl, void *dlg)
+void dlg_refresh(union control *ctrl, dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     int i, j;
     struct winctrl *c;
 
@@ -2467,19 +2439,17 @@ void dlg_refresh(union control *ctrl, void *dlg)
     }
 }
 
-void dlg_coloursel_start(union control *ctrl, void *dlg, int r, int g, int b)
+void dlg_coloursel_start(union control *ctrl, dlgparam *dp, int r, int g, int b)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     dp->coloursel_wanted = TRUE;
     dp->coloursel_result.r = r;
     dp->coloursel_result.g = g;
     dp->coloursel_result.b = b;
 }
 
-int dlg_coloursel_results(union control *ctrl, void *dlg,
+int dlg_coloursel_results(union control *ctrl, dlgparam *dp,
 			  int *r, int *g, int *b)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     if (dp->coloursel_result.ok) {
 	*r = dp->coloursel_result.r;
 	*g = dp->coloursel_result.g;
@@ -2489,9 +2459,8 @@ int dlg_coloursel_results(union control *ctrl, void *dlg,
 	return 0;
 }
 
-void dlg_auto_set_fixed_pitch_flag(void *dlg)
+void dlg_auto_set_fixed_pitch_flag(dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     Conf *conf = (Conf *)dp->data;
     FontSpec *fs;
     int quality;
@@ -2533,15 +2502,13 @@ void dlg_auto_set_fixed_pitch_flag(void *dlg)
         dp->fixed_pitch_fonts = FALSE;
 }
 
-int dlg_get_fixed_pitch_flag(void *dlg)
+int dlg_get_fixed_pitch_flag(dlgparam *dp)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     return dp->fixed_pitch_fonts;
 }
 
-void dlg_set_fixed_pitch_flag(void *dlg, int flag)
+void dlg_set_fixed_pitch_flag(dlgparam *dp, int flag)
 {
-    struct dlgparam *dp = (struct dlgparam *)dlg;
     dp->fixed_pitch_fonts = flag;
 }
 
diff --git a/windows/winstuff.h b/windows/winstuff.h
index 1ecec333..e57bf0da 100644
--- a/windows/winstuff.h
+++ b/windows/winstuff.h
@@ -437,9 +437,9 @@ void fwdsetter(struct ctlpos *cp, int listid, char *stext, int sid,
 	       char *btext, int bid,
 	       char *r1text, int r1id, char *r2text, int r2id);
 
-void dlg_auto_set_fixed_pitch_flag(void *dlg);
-int dlg_get_fixed_pitch_flag(void *dlg);
-void dlg_set_fixed_pitch_flag(void *dlg, int flag);
+void dlg_auto_set_fixed_pitch_flag(dlgparam *dlg);
+int dlg_get_fixed_pitch_flag(dlgparam *dlg);
+void dlg_set_fixed_pitch_flag(dlgparam *dlg, int flag);
 
 #define MAX_SHORTCUTS_PER_CTRL 16