diff --git a/servo/components/style/properties/longhand/font.mako.rs b/servo/components/style/properties/longhand/font.mako.rs
index 9ab48c9508f4e..9892445ee5f55 100644
--- a/servo/components/style/properties/longhand/font.mako.rs
+++ b/servo/components/style/properties/longhand/font.mako.rs
@@ -9898,6 +9898,25 @@ helpers
 :
 longhand
 >
+#
+[
+cfg
+(
+any
+(
+feature
+=
+"
+gecko
+"
+feature
+=
+"
+testing
+"
+)
+)
+]
 macro_rules
 !
 exclusive_value