diff --git a/util/ub_event_pluggable.c b/util/ub_event_pluggable.c
index 235bba6ba..4280d4db1 100644
--- a/util/ub_event_pluggable.c
+++ b/util/ub_event_pluggable.c
@@ -666,7 +666,8 @@ ub_winsock_tcp_wouldblock(struct ub_event* ev, int eventbits)
 		fptr_ok(ev->vmt != &default_event_vmt ||
 			ev->vmt->winsock_tcp_wouldblock ==
 			my_winsock_tcp_wouldblock);
-		(*ev->vmt->winsock_tcp_wouldblock)(ev, eventbits);
+		if (ev->vmt->winsock_tcp_wouldblock)
+			(*ev->vmt->winsock_tcp_wouldblock)(ev, eventbits);
 	}
 }