diff --git a/Shorewall-perl/Shorewall/Interfaces.pm b/Shorewall-perl/Shorewall/Interfaces.pm
index f1d8596be..d4dba4e19 100644
--- a/Shorewall-perl/Shorewall/Interfaces.pm
+++ b/Shorewall-perl/Shorewall/Interfaces.pm
@@ -266,7 +266,7 @@ sub validate_interfaces_file()
 	    @networks = @allipv4;
 	}
 
-	add_group_to_zone( $zone, $zoneref->{type}, $interface, \@networks, $optionsref ) if @networks;
+	add_group_to_zone( $zone, $zoneref->{type}, $interface, \@networks, $optionsref ) if $zone && @networks;
 
     	$interfaces{$interface}{zone} = $zone; #Must follow the call to add_group_to_zone()