diff --git a/src/polkitbackend/polkitbackendsessionmonitor-systemd.c b/src/polkitbackend/polkitbackendsessionmonitor-systemd.c
index 4b83edd..2a9a5d9 100644
--- a/src/polkitbackend/polkitbackendsessionmonitor-systemd.c
+++ b/src/polkitbackend/polkitbackendsessionmonitor-systemd.c
@@ -71,7 +71,8 @@ sd_source_dispatch (GSource     *source,
   SdSource *sd_source = (SdSource *)source;
   gboolean ret;
 
-  g_warn_if_fail (callback != NULL);
+  if (callback == NULL)
+    return G_SOURCE_CONTINUE;
 
   ret = (*callback) (user_data);