diff --git a/plugins/products b/plugins/products
index 72d0f40..f278f7a 100755
--- a/plugins/products
+++ b/plugins/products
@@ -21,8 +21,9 @@ sub command :Tab(edit) {
 
     for my $fields (@products) {
         next if $command ne $fields->[0];
+        next if $fields->[1] < 0;
 
-        $cart->add(undef, - $fields->[1], $fields->[2]);
+        $cart->add(undef, 0 - $fields->[1], $fields->[2]);
         return ACCEPT;
     }