diff --git a/desmume/src/gtk/main.cpp b/desmume/src/gtk/main.cpp
index d019f3317..c9c180488 100644
--- a/desmume/src/gtk/main.cpp
+++ b/desmume/src/gtk/main.cpp
@@ -68,6 +68,7 @@ static const char *bad_glob_cflash_disk_image_file;
#define SCREENS_PIXEL_SIZE (256*192*2)
#define SCREEN_BYTES_PER_PIXEL 3
+#define GAP_SIZE 50
#define FPS_LIMITER_FRAME_PERIOD 8
static SDL_sem *fps_limiter_semaphore;
@@ -104,7 +105,8 @@ static void ToggleStatusbarVisible(GtkToggleAction *action);
static void ToggleToolbarVisible(GtkToggleAction *action);
static void desmume_gtk_disable_audio (GtkToggleAction *action);
static void desmume_gtk_mic_noise (GtkToggleAction *action);
-static void SetRotation (GtkAction *action, gpointer data);
+static void ToggleGap (GtkToggleAction *action);
+static void SetRotation (GtkAction *action);
static void Modify_Layer(GtkToggleAction* action, gpointer data);
#ifdef DESMUME_GTK_FIRMWARE_BROKEN
static void SelectFirmwareFile();
@@ -198,6 +200,7 @@ static const char *ui_description =
" "
" "
" "
+" "
" "
"