diff --git a/src/k_menufunc.c b/src/k_menufunc.c
index 881b9b044..de474ae23 100644
--- a/src/k_menufunc.c
+++ b/src/k_menufunc.c
@@ -275,6 +275,14 @@ static boolean M_GamestateCanOpenMenu(void)
 //
 boolean M_Responder(event_t *ev)
 {
+	if (ev->type == ev_keydown && ev->data1 == KEY_F11 && !ev->data2)
+	{
+		// F11 can always be used to toggle fullscreen, it's
+		// a safe key.
+		CV_AddValue(&cv_fullscreen, 1);
+		return true;
+	}
+
 	if (dedicated
 		|| (demo.playback && demo.attract)
 		|| M_GamestateCanOpenMenu() == false)