diff --git a/src/event/Loop.cxx b/src/event/Loop.cxx
index 8cd4cde72..9c76c422c 100644
--- a/src/event/Loop.cxx
+++ b/src/event/Loop.cxx
@@ -100,7 +100,9 @@ EventLoop::RemoveIdle(IdleMonitor &i)
 void
 EventLoop::AddTimer(TimeoutMonitor &t, unsigned ms)
 {
-	assert(IsInsideOrVirgin());
+	/* can't use IsInsideOrVirgin() here because libavahi-client
+	   modifies the timeout during avahi_client_free() */
+	assert(IsInsideOrNull());
 
 	timers.insert(TimerRecord(t, now_ms + ms));
 	again = true;