diff --git a/src/popupwin.c b/src/popupwin.c
index efcc395..3b808e2 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -2599,7 +2599,7 @@
     win_T	*wp;
 
     wp = mouse_find_win(&row, &col, FIND_POPUP);
-    if (WIN_IS_POPUP(wp))
+    if (wp != NULL && WIN_IS_POPUP(wp))
 	rettv->vval.v_number = wp->w_id;
 }