diff --git a/src/gui.c b/src/gui.c
--- a/src/gui.c
+++ b/src/gui.c
@@ -1402,7 +1402,7 @@
      if (!gui.shell_created)
        return;

-#ifdef MSWIN
+#if defined(MSWIN) || defined(FEAT_GUI_GTK)
      /* If not setting to a user specified size and maximized, calculate the
       * number of characters that fit in the maximized window. */
      if (!mustset && gui_mch_maximized())
diff --git a/src/gui_gtk_x11.c b/src/gui_gtk_x11.c
--- a/src/gui_gtk_x11.c
+++ b/src/gui_gtk_x11.c
@@ -3901,6 +3901,17 @@
        gtk_window_unmaximize(GTK_WINDOW(gui.mainwin));
  }

+    void
+gui_mch_newfont()
+{
+    int w, h;
+
+    gtk_window_get_size(GTK_WINDOW(gui.mainwin), &w, &h);
+    w -= get_menu_tool_width();
+    h -= get_menu_tool_height();
+    gui_resize_shell(w, h);
+}
+
  /*
   * Set the windows size.
   */
diff --git a/src/proto/gui_gtk_x11.pro b/src/proto/gui_gtk_x11.pro
--- a/src/proto/gui_gtk_x11.pro
+++ b/src/proto/gui_gtk_x11.pro
@@ -20,6 +20,7 @@
  void gui_mch_set_winpos __ARGS((int x, int y));
  int gui_mch_maximized __ARGS((void));
  void gui_mch_unmaximize __ARGS((void));
+void gui_mch_newfont __ARGS((void));
  void gui_mch_set_shellsize __ARGS((int width, int height, int min_width, int min_height, int base_width, int 
base_height, int direction));
  void gui_mch_get_screen_dimensions __ARGS((int *screen_w, int *screen_h));
  void gui_mch_settitle __ARGS((char_u *title, char_u *icon));