diff --git a/cmdgen.c b/cmdgen.c
index eaaf2e48..8b39f1d8 100644
--- a/cmdgen.c
+++ b/cmdgen.c
@@ -619,7 +619,7 @@ int main(int argc, char **argv)
         (intype == SSH_KEYTYPE_SSHCOM && outtype == SSHCOM)) {
         if (!outfile) {
             outfile = infile;
-            outfiletmp = dupcat(outfile, ".tmp", NULL);
+            outfiletmp = dupcat(outfile, ".tmp");
         }
 
         if (!change_passphrase && !comment) {
diff --git a/config.c b/config.c
index a265dda5..db83adb4 100644
--- a/config.c
+++ b/config.c
@@ -1104,7 +1104,7 @@ static void environ_handler(union control *ctrl, dlgparam *dlg,
                 return;
             }
             conf_set_str_str(conf, CONF_environmt, key, val);
-            str = dupcat(key, "\t", val, NULL);
+            str = dupcat(key, "\t", val);
             dlg_editbox_set(ed->varbox, dlg, "");
             dlg_editbox_set(ed->valbox, dlg, "");
             sfree(str);
@@ -1235,7 +1235,7 @@ static void portfwd_handler(union control *ctrl, dlgparam *dlg,
                 val = dupstr("D");     /* special case */
             }
 
-            key = dupcat(family, type, src, NULL);
+            key = dupcat(family, type, src);
             sfree(src);
 
             if (conf_get_str_str_opt(conf, CONF_portfwd, key)) {
@@ -1402,7 +1402,7 @@ static void clipboard_selector_handler(union control *ctrl, dlgparam *dlg,
                 if (!strcmp(sval, options[i].name))
                     break;             /* needs escaping */
             if (i < lenof(options) || sval[0] == '=') {
-                char *escaped = dupcat("=", sval, (const char *)NULL);
+                char *escaped = dupcat("=", sval);
                 dlg_editbox_set(ctrl, dlg, escaped);
                 sfree(escaped);
             } else {
diff --git a/misc.h b/misc.h
index 6991d8e8..b9fb5721 100644
--- a/misc.h
+++ b/misc.h
@@ -41,7 +41,8 @@ char *host_strduptrim(const char *s);
 #endif /* __GNUC__ */
 
 char *dupstr(const char *s);
-char *dupcat(const char *s1, ...);
+char *dupcat_fn(const char *s1, ...);
+#define dupcat(...) dupcat_fn(__VA_ARGS__, (const char *)NULL)
 char *dupprintf(const char *fmt, ...)
 #ifdef __GNUC__
     __attribute__ ((format (PUTTY_PRINTF_ARCHETYPE, 1, 2)))
diff --git a/pscp.c b/pscp.c
index bcf18dcf..4724622d 100644
--- a/pscp.c
+++ b/pscp.c
@@ -120,7 +120,7 @@ static void tell_user(FILE *stream, const char *fmt, ...)
     va_start(ap, fmt);
     str = dupvprintf(fmt, ap);
     va_end(ap);
-    str2 = dupcat(str, "\n", NULL);
+    str2 = dupcat(str, "\n");
     sfree(str);
     abandon_stats();
     tell_str(stream, str2);
@@ -231,7 +231,7 @@ static NORETURN void bump(const char *fmt, ...)
     va_start(ap, fmt);
     str = dupvprintf(fmt, ap);
     va_end(ap);
-    str2 = dupcat(str, "\n", NULL);
+    str2 = dupcat(str, "\n");
     sfree(str);
     abandon_stats();
     tell_str(stderr, str2);
@@ -762,7 +762,7 @@ int scp_send_filename(const char *name, uint64_t size, int permissions)
         struct fxp_attrs attrs;
 
         if (scp_sftp_targetisdir) {
-            fullname = dupcat(scp_sftp_remotepath, "/", name, NULL);
+            fullname = dupcat(scp_sftp_remotepath, "/", name);
         } else {
             fullname = dupstr(scp_sftp_remotepath);
         }
@@ -917,7 +917,7 @@ int scp_send_dirname(const char *name, int modes)
         bool ret;
 
         if (scp_sftp_targetisdir) {
-            fullname = dupcat(scp_sftp_remotepath, "/", name, NULL);
+            fullname = dupcat(scp_sftp_remotepath, "/", name);
         } else {
             fullname = dupstr(scp_sftp_remotepath);
         }
@@ -1128,8 +1128,7 @@ int scp_get_sink_action(struct scp_sink_action *act)
             if (head->namepos < head->namelen) {
                 head->matched_something = true;
                 fname = dupcat(head->dirpath, "/",
-                               head->names[head->namepos++].filename,
-                               NULL);
+                               head->names[head->namepos++].filename);
                 must_free_fname = true;
             } else {
                 /*
@@ -1549,7 +1548,7 @@ static void run_err(const char *fmt, ...)
     va_start(ap, fmt);
     errs++;
     str = dupvprintf(fmt, ap);
-    str2 = dupcat("pscp: ", str, "\n", NULL);
+    str2 = dupcat("pscp: ", str, "\n");
     sfree(str);
     scp_send_errmsg(str2);
     abandon_stats();
@@ -1697,7 +1696,7 @@ static void rsource(const char *src)
     if (dir != NULL) {
         char *filename;
         while ((filename = read_filename(dir)) != NULL) {
-            char *foundfile = dupcat(src, "/", filename, NULL);
+            char *foundfile = dupcat(src, "/", filename);
             source(foundfile);
             sfree(foundfile);
             sfree(filename);
diff --git a/psftp.c b/psftp.c
index c0d2f9df..dd7edfd1 100644
--- a/psftp.c
+++ b/psftp.c
@@ -124,7 +124,7 @@ char *canonify(const char *name)
             slash = "";
         else
             slash = "/";
-        fullname = dupcat(pwd, slash, name, NULL);
+        fullname = dupcat(pwd, slash, name);
     }
 
     req = fxp_realpath_send(fullname);
@@ -203,8 +203,8 @@ char *canonify(const char *name)
          * component. Concatenate the last component and return.
          */
         returnname = dupcat(canonname,
-                            canonname[strlen(canonname) - 1] ==
-                            '/' ? "" : "/", fullname + i + 1, NULL);
+                            (strendswith(canonname, "/") ? "" : "/"),
+                            fullname + i + 1);
         sfree(fullname);
         sfree(canonname);
         return returnname;
@@ -376,7 +376,7 @@ bool sftp_get_file(char *fname, char *outfname, bool recurse, bool restart)
                 char *nextfname, *nextoutfname;
                 bool retd;
 
-                nextfname = dupcat(fname, "/", ournames[i]->filename, NULL);
+                nextfname = dupcat(fname, "/", ournames[i]->filename);
                 nextoutfname = dir_file_cat(outfname, ournames[i]->filename);
                 retd = sftp_get_file(
                     nextfname, nextoutfname, recurse, restart);
@@ -601,7 +601,7 @@ bool sftp_put_file(char *fname, char *outfname, bool recurse, bool restart)
         if (restart) {
             while (i < nnames) {
                 char *nextoutfname;
-                nextoutfname = dupcat(outfname, "/", ournames[i], NULL);
+                nextoutfname = dupcat(outfname, "/", ournames[i]);
                 req = fxp_stat_send(nextoutfname);
                 pktin = sftp_wait_for_reply(req);
                 result = fxp_stat_recv(pktin, req, &attrs);
@@ -625,7 +625,7 @@ bool sftp_put_file(char *fname, char *outfname, bool recurse, bool restart)
             bool retd;
 
             nextfname = dir_file_cat(fname, ournames[i]);
-            nextoutfname = dupcat(outfname, "/", ournames[i], NULL);
+            nextoutfname = dupcat(outfname, "/", ournames[i]);
             retd = sftp_put_file(nextfname, nextoutfname, recurse, restart);
             restart = false;           /* after first partial file, do full */
             sfree(nextoutfname);
@@ -1557,7 +1557,7 @@ static bool sftp_action_mv(void *vctx, char *srcfname)
 
         p = srcfname + strlen(srcfname);
         while (p > srcfname && p[-1] != '/') p--;
-        newname = dupcat(ctx->dstfname, "/", p, NULL);
+        newname = dupcat(ctx->dstfname, "/", p);
         newcanon = canonify(newname);
         sfree(newname);
 
diff --git a/settings.c b/settings.c
index d7c85e23..7bf7e4d2 100644
--- a/settings.c
+++ b/settings.c
@@ -490,8 +490,7 @@ static void write_clip_setting(settings_w *sesskey, const char *savekey,
         break;
       case CLIPUI_CUSTOM:
         {
-            char *sval = dupcat("custom:", conf_get_str(conf, strconfkey),
-                                (const char *)NULL);
+            char *sval = dupcat("custom:", conf_get_str(conf, strconfkey));
             write_setting_s(sesskey, savekey, sval);
             sfree(sval);
         }
diff --git a/ssh2transport.c b/ssh2transport.c
index e577c5ac..223ec5b7 100644
--- a/ssh2transport.c
+++ b/ssh2transport.c
@@ -1200,9 +1200,7 @@ static void ssh2_transport_process_queue(PacketProtocolLayer *ppl)
             if (better) {
                 if (betteralgs) {
                     char *old_ba = betteralgs;
-                    betteralgs = dupcat(betteralgs, ",",
-                                        hktype->alg->ssh_id,
-                                        (const char *)NULL);
+                    betteralgs = dupcat(betteralgs, ",", hktype->alg->ssh_id);
                     sfree(old_ba);
                 } else {
                     betteralgs = dupstr(hktype->alg->ssh_id);
diff --git a/sshgssc.c b/sshgssc.c
index adbb4377..d9f62c39 100644
--- a/sshgssc.c
+++ b/sshgssc.c
@@ -25,7 +25,7 @@ static Ssh_gss_stat ssh_gssapi_import_name(struct ssh_gss_library *lib,
     gss_buffer_desc host_buf;
     char *pStr;
 
-    pStr = dupcat("host@", host, NULL);
+    pStr = dupcat("host@", host);
 
     host_buf.value = pStr;
     host_buf.length = strlen(pStr);
diff --git a/sshshare.c b/sshshare.c
index 4d124187..24f4c125 100644
--- a/sshshare.c
+++ b/sshshare.c
@@ -1858,7 +1858,7 @@ static void share_listen_closing(Plug *plug, const char *error_msg,
 static void share_send_verstring(ssh_sharing_connstate *cs)
 {
     char *fullstring = dupcat("SSHCONNECTION@putty.projects.tartarus.org-2.0-",
-                              cs->parent->server_verstring, "\015\012", NULL);
+                              cs->parent->server_verstring, "\015\012");
     sk_write(cs->sock, fullstring, strlen(fullstring));
     sfree(fullstring);
 
diff --git a/unix/gtkdlg.c b/unix/gtkdlg.c
index cd3f8092..c44f9306 100644
--- a/unix/gtkdlg.c
+++ b/unix/gtkdlg.c
@@ -3654,7 +3654,7 @@ void old_keyfile_warning(void)
 
 void nonfatal_message_box(void *window, const char *msg)
 {
-    char *title = dupcat(appname, " Error", NULL);
+    char *title = dupcat(appname, " Error");
     create_message_box(
         window, title, msg,
         string_width("REASONABLY LONG LINE OF TEXT FOR BASIC SANITY"),
@@ -3694,7 +3694,7 @@ static void licence_clicked(GtkButton *button, gpointer data)
 {
     char *title;
 
-    title = dupcat(appname, " Licence", NULL);
+    title = dupcat(appname, " Licence");
     assert(aboutbox != NULL);
     create_message_box(aboutbox, title, LICENCE_TEXT("\n\n"),
                        string_width("LONGISH LINE OF TEXT SO THE LICENCE"
@@ -3716,7 +3716,7 @@ void about_box(void *window)
 
     aboutbox = our_dialog_new();
     gtk_container_set_border_width(GTK_CONTAINER(aboutbox), 10);
-    title = dupcat("About ", appname, NULL);
+    title = dupcat("About ", appname);
     gtk_window_set_title(GTK_WINDOW(aboutbox), title);
     sfree(title);
 
@@ -3932,7 +3932,7 @@ void showeventlog(eventlog_stuff *es, void *parentwin)
     c->listbox.percentages[2] = 65;
 
     es->window = window = our_dialog_new();
-    title = dupcat(appname, " Event Log", (const char *)NULL);
+    title = dupcat(appname, " Event Log");
     gtk_window_set_title(GTK_WINDOW(window), title);
     sfree(title);
     w0 = layout_ctrls(&es->dp, NULL, &es->scs, s0, GTK_WINDOW(window));
@@ -4025,7 +4025,7 @@ void logevent_dlg(eventlog_stuff *es, const char *string)
     strftime(timebuf, sizeof(timebuf), "%Y-%m-%d %H:%M:%S\t", &tm);
 
     sfree(*location);
-    *location = dupcat(timebuf, string, NULL);
+    *location = dupcat(timebuf, string);
     if (es->window) {
         dlg_listbox_add(es->listctrl, &es->dp, *location);
     }
diff --git a/unix/gtkfont.c b/unix/gtkfont.c
index db3dc589..4e62fb34 100644
--- a/unix/gtkfont.c
+++ b/unix/gtkfont.c
@@ -461,7 +461,7 @@ static unifont *x11font_create(GtkWidget *widget, const char *name,
         reg = XGetAtomName(disp, (Atom)registry_ret);
         enc = XGetAtomName(disp, (Atom)encoding_ret);
         if (reg && enc) {
-            char *encoding = dupcat(reg, "-", enc, NULL);
+            char *encoding = dupcat(reg, "-", enc);
             pubcs = realcs = charset_from_xenc(encoding);
 
             /*
@@ -1280,8 +1280,7 @@ static char *x11font_size_increment(unifont *font, int increment)
         if (xlfd_best) {
             char *bare_returned_name = xlfd_recompose(xlfd_best);
             returned_name = dupcat(
-                xfont->u.vt->prefix, ":", bare_returned_name,
-                (const char *)NULL);
+                xfont->u.vt->prefix, ":", bare_returned_name);
             sfree(bare_returned_name);
         }
 
@@ -2042,8 +2041,7 @@ static char *pangofont_size_increment(unifont *font, int increment)
     } else {
         pango_font_description_set_size(desc, size);
         newname = pango_font_description_to_string(desc);
-        retname = dupcat(pfont->u.vt->prefix, ":",
-                         newname, (const char *)NULL);
+        retname = dupcat(pfont->u.vt->prefix, ":", newname);
         g_free(newname);
     }
 
@@ -3780,15 +3778,14 @@ char *unifontsel_get_name(unifontsel *fontsel)
         name = fs->selected->fontclass->scale_fontname
             (GTK_WIDGET(fs->u.window), fs->selected->realname, fs->selsize);
         if (name) {
-            char *ret = dupcat(fs->selected->fontclass->prefix, ":",
-                               name, NULL);
+            char *ret = dupcat(fs->selected->fontclass->prefix, ":", name);
             sfree(name);
             return ret;
         }
     }
 
     return dupcat(fs->selected->fontclass->prefix, ":",
-                  fs->selected->realname, NULL);
+                  fs->selected->realname);
 }
 
 #endif /* GTK_CHECK_VERSION(2,0,0) */
diff --git a/unix/gtkwin.c b/unix/gtkwin.c
index 0da96184..31787237 100644
--- a/unix/gtkwin.c
+++ b/unix/gtkwin.c
@@ -235,7 +235,7 @@ static void post_fatal_message_box(void *vctx, int result)
 static void common_connfatal_message_box(
     GtkFrontend *inst, const char *msg, post_dialog_fn_t postfn)
 {
-    char *title = dupcat(appname, " Fatal Error", NULL);
+    char *title = dupcat(appname, " Fatal Error");
     GtkWidget *dialog = create_message_box(
         inst->window, title, msg,
         string_width("REASONABLY LONG LINE OF TEXT FOR BASIC SANITY"),
@@ -661,7 +661,7 @@ gint delete_window(GtkWidget *widget, GdkEvent *event, GtkFrontend *inst)
          * case we'll just re-emphasise that one.
          */
         if (!find_and_raise_dialog(inst, DIALOG_SLOT_WARN_ON_CLOSE)) {
-            char *title = dupcat(appname, " Exit Confirmation", NULL);
+            char *title = dupcat(appname, " Exit Confirmation");
             GtkWidget *dialog = create_message_box(
                 inst->window, title,
                 "Are you sure you want to close this session?",
@@ -1080,8 +1080,7 @@ gint key_event(GtkWidget *widget, GdkEventKey *event, gpointer data)
                     char *old = state_string;
                     state_string = dupcat(state_string,
                                           state_string[0] ? "|" : "",
-                                          mod_bits[i].name,
-                                          (char *)NULL);
+                                          mod_bits[i].name);
                     sfree(old);
 
                     val &= ~mod_bits[i].mod_bit;
@@ -4596,7 +4595,7 @@ void change_settings_menuitem(GtkMenuItem *item, gpointer data)
     if (find_and_raise_dialog(inst, DIALOG_SLOT_RECONFIGURE))
         return;
 
-    title = dupcat(appname, " Reconfiguration", NULL);
+    title = dupcat(appname, " Reconfiguration");
 
     ctx = snew(struct after_change_settings_dialog_ctx);
     ctx->inst = inst;
@@ -5489,7 +5488,7 @@ void new_session_window(Conf *conf, const char *geometry_string)
                    paste_clipboard_menuitem);
         MKMENUITEM("Copy All", copy_all_menuitem);
         MKSEP();
-        s = dupcat("About ", appname, NULL);
+        s = dupcat("About ", appname);
         MKMENUITEM(s, about_menuitem);
         sfree(s);
 #undef MKMENUITEM
diff --git a/unix/ux_x11.c b/unix/ux_x11.c
index bef036b4..7a0c2218 100644
--- a/unix/ux_x11.c
+++ b/unix/ux_x11.c
@@ -27,7 +27,7 @@ void platform_get_x11_auth(struct X11Display *disp, Conf *conf)
     if (!xauthfile) {
         xauthfile = getenv("HOME");
         if (xauthfile) {
-            xauthfile = dupcat(xauthfile, "/.Xauthority", NULL);
+            xauthfile = dupcat(xauthfile, "/.Xauthority");
             needs_free = true;
         }
     }
@@ -127,7 +127,7 @@ int platform_make_x11_server(Plug *plug, const char *progname, int mindisp,
     if (!tmpdir || !*tmpdir)
         tmpdir = "/tmp";
 
-    authfilename = dupcat(tmpdir, "/", progname, "-Xauthority-XXXXXX", NULL);
+    authfilename = dupcat(tmpdir, "/", progname, "-Xauthority-XXXXXX");
 
     {
         int oldumask = umask(077);
diff --git a/unix/uxpgnt.c b/unix/uxpgnt.c
index 9c5f4942..61a94334 100644
--- a/unix/uxpgnt.c
+++ b/unix/uxpgnt.c
@@ -329,7 +329,7 @@ static char *askpass_tty(const char *prompt)
     p->to_server = false;
     p->from_server = false;
     p->name = dupstr("Pageant passphrase prompt");
-    add_prompt(p, dupcat(prompt, ": ", (const char *)NULL), false);
+    add_prompt(p, dupcat(prompt, ": "), false);
     ret = console_get_userpass_input(p);
     assert(ret >= 0);
 
diff --git a/unix/uxpty.c b/unix/uxpty.c
index e57770f5..2533d958 100644
--- a/unix/uxpty.c
+++ b/unix/uxpty.c
@@ -1134,7 +1134,7 @@ Backend *pty_backend_create(
             for (val = conf_get_str_strs(conf, CONF_environmt, NULL, &key);
                  val != NULL;
                  val = conf_get_str_strs(conf, CONF_environmt, key, &key)) {
-                char *varval = dupcat(key, "=", val, NULL);
+                char *varval = dupcat(key, "=", val);
                 putenv(varval);
                 /*
                  * We must not free varval, since putenv links it
diff --git a/unix/uxputty.c b/unix/uxputty.c
index 8142bdd0..7449c3ab 100644
--- a/unix/uxputty.c
+++ b/unix/uxputty.c
@@ -47,7 +47,7 @@ const struct BackendVtable *select_backend(Conf *conf)
 
 void initial_config_box(Conf *conf, post_dialog_fn_t after, void *afterctx)
 {
-    char *title = dupcat(appname, " Configuration", NULL);
+    char *title = dupcat(appname, " Configuration");
     create_config_box(title, conf, false, 0, after, afterctx);
     sfree(title);
 }
@@ -57,7 +57,7 @@ const bool dup_check_launchable = true;
 
 char *make_default_wintitle(char *hostname)
 {
-    return dupcat(hostname, " - ", appname, NULL);
+    return dupcat(hostname, " - ", appname);
 }
 
 /*
diff --git a/unix/uxsftp.c b/unix/uxsftp.c
index de838f88..3195f902 100644
--- a/unix/uxsftp.c
+++ b/unix/uxsftp.c
@@ -460,7 +460,7 @@ char *dir_file_cat(const char *dir, const char *file)
     ptrlen dir_pl = ptrlen_from_asciz(dir);
     return dupcat(
         dir, ptrlen_endswith(dir_pl, PTRLEN_LITERAL("/"), NULL) ? "" : "/",
-        file, NULL);
+        file);
 }
 
 /*
diff --git a/unix/uxshare.c b/unix/uxshare.c
index 0c5265bf..f1ef2019 100644
--- a/unix/uxshare.c
+++ b/unix/uxshare.c
@@ -273,7 +273,7 @@ int platform_ssh_share(const char *pi_name, Conf *conf,
     /*
      * Acquire a lock on a file in that directory.
      */
-    lockname = dupcat(dirname, "/lock", (char *)NULL);
+    lockname = dupcat(dirname, "/lock");
     lockfd = open(lockname, O_CREAT | O_RDWR | O_TRUNC, 0600);
     if (lockfd < 0) {
         *logtext = dupprintf("%s: open: %s", lockname, strerror(errno));
@@ -348,11 +348,11 @@ void platform_ssh_share_cleanup(const char *name)
         return;
     }
 
-    filename = dupcat(dirname, "/socket", (char *)NULL);
+    filename = dupcat(dirname, "/socket");
     remove(filename);
     sfree(filename);
 
-    filename = dupcat(dirname, "/lock", (char *)NULL);
+    filename = dupcat(dirname, "/lock");
     remove(filename);
     sfree(filename);
 
diff --git a/unix/uxstore.c b/unix/uxstore.c
index 250db9a8..b3a5b8a7 100644
--- a/unix/uxstore.c
+++ b/unix/uxstore.c
@@ -449,7 +449,7 @@ FontSpec *read_setting_fontspec(settings_r *handle, const char *name)
      * provided name string (e.g. "Font") to a suffixed one
      * ("FontName").
      */
-    char *suffname = dupcat(name, "Name", NULL);
+    char *suffname = dupcat(name, "Name");
     char *tmp;
 
     if ((tmp = read_setting_s(handle, suffname)) != NULL) {
@@ -463,7 +463,7 @@ FontSpec *read_setting_fontspec(settings_r *handle, const char *name)
     /* Fall back to old-style name. */
     tmp = read_setting_s(handle, name);
     if (tmp && *tmp) {
-        char *tmp2 = dupcat("server:", tmp, NULL);
+        char *tmp2 = dupcat("server:", tmp);
         FontSpec *fs = fontspec_new(tmp2);
         sfree(tmp2);
         sfree(tmp);
@@ -491,7 +491,7 @@ void write_setting_fontspec(settings_w *handle, const char *name, FontSpec *fs)
      * writing our settings back out we simply always generate the
      * new-style name.
      */
-    char *suffname = dupcat(name, "Name", NULL);
+    char *suffname = dupcat(name, "Name");
     write_setting_s(handle, suffname, fs->name);
     sfree(suffname);
 }
diff --git a/utils.c b/utils.c
index 18193960..6cd1cf4c 100644
--- a/utils.c
+++ b/utils.c
@@ -249,7 +249,7 @@ char *dupstr(const char *s)
 }
 
 /* Allocate the concatenation of N strings. Terminate arg list with NULL. */
-char *dupcat(const char *s1, ...)
+char *dupcat_fn(const char *s1, ...)
 {
     int len;
     char *p, *q, *sn;
diff --git a/windows/windlg.c b/windows/windlg.c
index faa56935..26bea503 100644
--- a/windows/windlg.c
+++ b/windows/windlg.c
@@ -776,7 +776,7 @@ static void win_gui_eventlog(LogPolicy *lp, const char *string)
 
     if (*location)
         sfree(*location);
-    *location = dupcat(timebuf, string, (const char *)NULL);
+    *location = dupcat(timebuf, string);
     if (logbox) {
         int count;
         SendDlgItemMessage(logbox, IDN_LIST, LB_ADDSTRING,
diff --git a/windows/wingss.c b/windows/wingss.c
index 6744475b..10e6d2db 100644
--- a/windows/wingss.c
+++ b/windows/wingss.c
@@ -308,7 +308,7 @@ static Ssh_gss_stat ssh_sspi_import_name(struct ssh_gss_library *lib,
     if (host == NULL) return SSH_GSS_FAILURE;
 
     /* copy it into form host/FQDN */
-    pStr = dupcat("host/", host, NULL);
+    pStr = dupcat("host/", host);
 
     *srv_name = (Ssh_gss_name) pStr;
 
diff --git a/windows/winjump.c b/windows/winjump.c
index 595bbe08..358504fd 100644
--- a/windows/winjump.c
+++ b/windows/winjump.c
@@ -432,7 +432,7 @@ static IShellLink *make_shell_link(const char *appname,
          * behaviour change in which an argument string starting with
          * '@' causes the SetArguments method to silently do the wrong
          * thing. */
-        param_string = dupcat(" @", sessionname, NULL);
+        param_string = dupcat(" @", sessionname);
     } else {
         param_string = dupstr("");
     }
@@ -440,8 +440,7 @@ static IShellLink *make_shell_link(const char *appname,
     sfree(param_string);
 
     if (sessionname) {
-        desc_string = dupcat("Connect to PuTTY session '",
-                             sessionname, "'", NULL);
+        desc_string = dupcat("Connect to PuTTY session '", sessionname, "'");
     } else {
         assert(appname);
         desc_string = dupprintf("Run %.*s",
diff --git a/windows/winmisc.c b/windows/winmisc.c
index 9ccb65fd..8cbdda08 100644
--- a/windows/winmisc.c
+++ b/windows/winmisc.c
@@ -233,7 +233,7 @@ HMODULE load_system32_dll(const char *libname)
             sgrowarray(sysdir, sysdirsize, len);
     }
 
-    fullpath = dupcat(sysdir, "\\", libname, NULL);
+    fullpath = dupcat(sysdir, "\\", libname);
     ret = LoadLibrary(fullpath);
     sfree(fullpath);
     return ret;
diff --git a/windows/winpgnt.c b/windows/winpgnt.c
index 718feb9f..0dbf32e8 100644
--- a/windows/winpgnt.c
+++ b/windows/winpgnt.c
@@ -451,7 +451,7 @@ static void prompt_add_keyfile(void)
             char *dir = filelist;
             char *filewalker = filelist + strlen(dir) + 1;
             while (*filewalker != '\0') {
-                char *filename = dupcat(dir, "\\", filewalker, NULL);
+                char *filename = dupcat(dir, "\\", filewalker);
                 Filename *fn = filename_from_str(filename);
                 win_add_keyfile(fn);
                 filename_free(fn);
diff --git a/windows/winsftp.c b/windows/winsftp.c
index ab323404..b120890c 100644
--- a/windows/winsftp.c
+++ b/windows/winsftp.c
@@ -274,7 +274,7 @@ DirHandle *open_directory(const char *name, const char **errmsg)
     DirHandle *ret;
 
     /* Enumerate files in dir `foo'. */
-    findfile = dupcat(name, "/*", NULL);
+    findfile = dupcat(name, "/*");
     h = FindFirstFile(findfile, &fdat);
     if (h == INVALID_HANDLE_VALUE) {
         *errmsg = win_strerror(GetLastError());
@@ -395,7 +395,7 @@ WildcardMatcher *begin_wildcard_matching(const char *name)
          (fdat.cFileName[1] == '.' && fdat.cFileName[2] == '\0')))
         ret->name = NULL;
     else
-        ret->name = dupcat(ret->srcpath, fdat.cFileName, NULL);
+        ret->name = dupcat(ret->srcpath, fdat.cFileName);
 
     return ret;
 }
@@ -413,7 +413,7 @@ char *wildcard_get_filename(WildcardMatcher *dir)
              (fdat.cFileName[1] == '.' && fdat.cFileName[2] == '\0')))
             dir->name = NULL;
         else
-            dir->name = dupcat(dir->srcpath, fdat.cFileName, NULL);
+            dir->name = dupcat(dir->srcpath, fdat.cFileName);
     }
 
     if (dir->name) {
@@ -455,7 +455,7 @@ char *dir_file_cat(const char *dir, const char *file)
     return dupcat(
         dir, (ptrlen_endswith(dir_pl, PTRLEN_LITERAL("\\"), NULL) ||
               ptrlen_endswith(dir_pl, PTRLEN_LITERAL("/"), NULL)) ? "" : "\\",
-        file, NULL);
+        file);
 }
 
 /* ----------------------------------------------------------------------
diff --git a/windows/winstore.c b/windows/winstore.c
index 1fba6ddb..09e5c028 100644
--- a/windows/winstore.c
+++ b/windows/winstore.c
@@ -175,7 +175,7 @@ FontSpec *read_setting_fontspec(settings_r *handle, const char *name)
     if (!fontname)
         return NULL;
 
-    settingname = dupcat(name, "IsBold", NULL);
+    settingname = dupcat(name, "IsBold");
     isbold = read_setting_i(handle, settingname, -1);
     sfree(settingname);
     if (isbold == -1) {
@@ -183,7 +183,7 @@ FontSpec *read_setting_fontspec(settings_r *handle, const char *name)
         return NULL;
     }
 
-    settingname = dupcat(name, "CharSet", NULL);
+    settingname = dupcat(name, "CharSet");
     charset = read_setting_i(handle, settingname, -1);
     sfree(settingname);
     if (charset == -1) {
@@ -191,7 +191,7 @@ FontSpec *read_setting_fontspec(settings_r *handle, const char *name)
         return NULL;
     }
 
-    settingname = dupcat(name, "Height", NULL);
+    settingname = dupcat(name, "Height");
     height = read_setting_i(handle, settingname, INT_MIN);
     sfree(settingname);
     if (height == INT_MIN) {
@@ -210,13 +210,13 @@ void write_setting_fontspec(settings_w *handle,
     char *settingname;
 
     write_setting_s(handle, name, font->name);
-    settingname = dupcat(name, "IsBold", NULL);
+    settingname = dupcat(name, "IsBold");
     write_setting_i(handle, settingname, font->isbold);
     sfree(settingname);
-    settingname = dupcat(name, "CharSet", NULL);
+    settingname = dupcat(name, "CharSet");
     write_setting_i(handle, settingname, font->charset);
     sfree(settingname);
-    settingname = dupcat(name, "Height", NULL);
+    settingname = dupcat(name, "Height");
     write_setting_i(handle, settingname, font->height);
     sfree(settingname);
 }
@@ -551,15 +551,13 @@ static HANDLE access_random_seed(int action)
         char profile[MAX_PATH + 1];
         if (SUCCEEDED(p_SHGetFolderPathA(NULL, CSIDL_LOCAL_APPDATA,
                                          NULL, SHGFP_TYPE_CURRENT, profile)) &&
-            try_random_seed_and_free(dupcat(profile, "\\PUTTY.RND",
-                                            (const char *)NULL),
+            try_random_seed_and_free(dupcat(profile, "\\PUTTY.RND"),
                                      action, &rethandle))
             return rethandle;
 
         if (SUCCEEDED(p_SHGetFolderPathA(NULL, CSIDL_APPDATA,
                                          NULL, SHGFP_TYPE_CURRENT, profile)) &&
-            try_random_seed_and_free(dupcat(profile, "\\PUTTY.RND",
-                                            (const char *)NULL),
+            try_random_seed_and_free(dupcat(profile, "\\PUTTY.RND"),
                                      action, &rethandle))
             return rethandle;
     }
@@ -582,8 +580,7 @@ static HANDLE access_random_seed(int action)
 
         if (drvlen < lenof(drv) && pathlen < lenof(path) && pathlen > 0 &&
             try_random_seed_and_free(
-                dupcat(drv, path, "\\PUTTY.RND", (const char *)NULL),
-                action, &rethandle))
+                dupcat(drv, path, "\\PUTTY.RND"), action, &rethandle))
             return rethandle;
     }
 
@@ -595,8 +592,7 @@ static HANDLE access_random_seed(int action)
         DWORD len = GetWindowsDirectory(windir, sizeof(windir));
         if (len < lenof(windir) &&
             try_random_seed_and_free(
-                dupcat(windir, "\\PUTTY.RND", (const char *)NULL),
-                action, &rethandle))
+                dupcat(windir, "\\PUTTY.RND"), action, &rethandle))
             return rethandle;
     }