diff --git a/Shorewall/firewall b/Shorewall/firewall
index 30630ce3b..4697bbf3e 100755
--- a/Shorewall/firewall
+++ b/Shorewall/firewall
@@ -5773,8 +5773,7 @@ setup_masq()
 	    networks="${networks%!*}"
 	fi
 
-
-	source="$networks"
+	source="${networks:=0.0.0.0/0}"
 
 	case $source in
 	*.*.*|+*|!+*)