diff --git a/PVE/VZDump.pm b/PVE/VZDump.pm
index 9ed0a173..d951e79a 100644
--- a/PVE/VZDump.pm
+++ b/PVE/VZDump.pm
@@ -351,7 +351,7 @@ sub read_vzdump_defaults {
     }
 
     foreach my $key (keys %$defaults) {
-	$res->{$key} = $defaults->{$key} if !$res->{$key};
+	$res->{$key} = $defaults->{$key} if !defined($res->{$key});
     }
 
     return $res;