diff --git a/ntp_sources.c b/ntp_sources.c
index 850f471..c32c822 100644
--- a/ntp_sources.c
+++ b/ntp_sources.c
@@ -996,7 +996,7 @@ NSR_GetName(IPAddr *address)
   int slot;
 
   if (!find_slot(address, &slot))
-    return 0;
+    return NULL;
 
   record = get_record(slot);
   if (record->name)