diff --git a/ui/vnc.c b/ui/vnc.c
index 14289fd951..10a272450b 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -3248,6 +3248,7 @@ char *vnc_display_local_addr(const char *id)
 {
     VncDisplay *vs = vnc_display_find(id);
 
+    assert(vs);
     return vnc_socket_local_addr("%s:%s", vs->lsock);
 }