diff --git a/unix/gtkdlg.c b/unix/gtkdlg.c
index 4389b592..3b7d9ab5 100644
--- a/unix/gtkdlg.c
+++ b/unix/gtkdlg.c
@@ -1084,7 +1084,7 @@ static void set_transient_window_pos(GtkWidget *parent, GtkWidget *child)
 #endif
 }
 
-static void trivial_post_dialog_fn(void *vctx, int result)
+void trivial_post_dialog_fn(void *vctx, int result)
 {
 }
 
diff --git a/unix/gtkwin.c b/unix/gtkwin.c
index 1b5fc86e..ffb4040d 100644
--- a/unix/gtkwin.c
+++ b/unix/gtkwin.c
@@ -4167,10 +4167,10 @@ static void after_change_settings_dialog(void *vctx, int retval)
                 char *msgboxtext =
                     dupprintf("Could not change fonts in terminal window: %s\n",
                               errmsg);
-                message_box(inst->window, "Font setup error", msgboxtext,
-                            string_width("Could not change fonts in terminal"
-                                         " window:"),
-                            FALSE, &buttons_ok);
+                create_message_box(
+                    inst->window, "Font setup error", msgboxtext,
+                    string_width("Could not change fonts in terminal window:"),
+                    FALSE, &buttons_ok, trivial_post_dialog_fn, NULL);
                 sfree(msgboxtext);
                 sfree(errmsg);
             } else {
diff --git a/unix/unix.h b/unix/unix.h
index 35941ebe..2d9600c4 100644
--- a/unix/unix.h
+++ b/unix/unix.h
@@ -122,8 +122,9 @@ unsigned long getticks(void);
 /* The per-session frontend structure managed by gtkwin.c */
 struct gui_data;
 
-/* Callback when a dialog box finishes */
+/* Callback when a dialog box finishes, and a no-op implementation of it */
 typedef void (*post_dialog_fn_t)(void *ctx, int result);
+void trivial_post_dialog_fn(void *vctx, int result);
 
 /* Start up a session window, with or without a preliminary config box */
 void initial_config_box(Conf *conf, post_dialog_fn_t after, void *afterctx);
@@ -189,9 +190,6 @@ GtkWidget *create_message_box(
     GtkWidget *parentwin, const char *title, const char *msg, int minwid,
     int selectable, const struct message_box_buttons *buttons,
     post_dialog_fn_t after, void *afterctx);
-int message_box(
-    GtkWidget *parentwin, const char *title, const char *msg, int minwid,
-    int selectable, const struct message_box_buttons *buttons);
 #endif
 
 /* Things pterm.c needs from {ptermm,uxputty}.c */