diff --git a/configure.ac b/configure.ac
index 1d614d31..9548ba87 100644
--- a/configure.ac
+++ b/configure.ac
@@ -122,17 +122,28 @@ case "$gtk_version_desired:$gtk" in
     # manual check for gtk1
     AC_PATH_PROG(GTK1_CONFIG, gtk-config, absent)
     if test "$GTK1_CONFIG" != "absent"; then
-      # the gtk1 headers need -std=gnu89, which flips round the
-      # definitions of 'inline' and 'extern inline' to their old GNU
-      # semantics before C99 chose different ones
-      GTK_CFLAGS="`"$GTK1_CONFIG" --cflags` -std=gnu89"
+      GTK_CFLAGS="`"$GTK1_CONFIG" --cflags`"
       GTK_LIBS=`"$GTK1_CONFIG" --libs`
+      AC_SUBST(GTK_CFLAGS)
+      AC_SUBST(GTK_LIBS)
       gtk=1
     fi
     ])
     ;;
 esac
 
+case "$gtk" in
+  1)
+    # Add some manual #defines to make the GTK 1 headers work when
+    # compiling in C99 mode. Left to themselves, they'll expect the
+    # old-style pre-C99 GNU semantics of 'inline' and 'extern inline',
+    # with the effect that they'll end up defining out-of-line
+    # versions of the inlined functions in more than one translation
+    # unit and cause a link failure. Override them to 'static inline',
+    # which is safe.
+    GTK_CFLAGS="$GTK_CFLAGS -DG_INLINE_FUNC='static inline' -DG_CAN_INLINE=1"
+esac
+
 AM_CONDITIONAL(HAVE_GTK, [test "$gtk" != "none"])
 
 if test "$gtk" = "2" -o "$gtk" = "3"; then
diff --git a/unix/gtkwin.c b/unix/gtkwin.c
index f954279f..bf0d9582 100644
--- a/unix/gtkwin.c
+++ b/unix/gtkwin.c
@@ -990,7 +990,6 @@ gint key_event(GtkWidget *widget, GdkEventKey *event, gpointer data)
     wchar_t ucsoutput[2];
     int ucsval, start, end, output_charset;
     bool special, use_ucsoutput;
-    bool nethack_mode, app_keypad_mode;
     bool force_format_numeric_keypad = false;
     bool generated_something = false;
     char num_keypad_key = '\0';
@@ -1392,10 +1391,6 @@ gint key_event(GtkWidget *widget, GdkEventKey *event, gpointer data)
 	special = false;
 	use_ucsoutput = false;
 
-        nethack_mode = conf_get_bool(inst->conf, CONF_nethack_keypad);
-        app_keypad_mode = (inst->term->app_keypad_keys &&
-                           !conf_get_bool(inst->conf, CONF_no_applic_k));
-
 	/* ALT+things gives leading Escape. */
 	output[0] = '\033';
 #if !GTK_CHECK_VERSION(2,0,0)
@@ -1418,6 +1413,10 @@ gint key_event(GtkWidget *widget, GdkEventKey *event, gpointer data)
          * it to.
          */
         bool numeric = false;
+        bool nethack_mode = conf_get_bool(inst->conf, CONF_nethack_keypad);
+        bool app_keypad_mode = (inst->term->app_keypad_keys &&
+                                !conf_get_bool(inst->conf, CONF_no_applic_k));
+
         switch (event->keyval) {
           case GDK_KEY_Num_Lock: num_keypad_key = 'G'; break;
           case GDK_KEY_KP_Divide: num_keypad_key = '/'; break;