diff --git a/src/display.c b/src/display.c
index dafecc96415240a7c31a449486f12763f2f226df..9144e160b11fc383b14324788fe42f4abd760dfc 100644
--- a/src/display.c
+++ b/src/display.c
@@ -424,6 +424,8 @@ myDisplayGrabServer (DisplayInfo *display)
 void
 myDisplayUngrabServer (DisplayInfo *display)
 {
+    g_return_if_fail (display);
+
     DBG ("entering myDisplayUngrabServer");
     display->xgrabcount = display->xgrabcount - 1;
     if (display->xgrabcount < 0)       /* should never happen */