diff --git a/src/js/static-ext-filtering.js b/src/js/static-ext-filtering.js
index 724a69e0f..da48cdf84 100644
--- a/src/js/static-ext-filtering.js
+++ b/src/js/static-ext-filtering.js
@@ -753,7 +753,7 @@
         if ( anchorLen > 4 ) { return false; }
         if (
             anchorLen > 1 &&
-            /^@?(?:\$\??|%|\?)$/.test(raw.slice(lpos + 1, rpos)) === false
+            /^@?(?:\$\??|%|\?)?$/.test(raw.slice(lpos + 1, rpos)) === false
         ) {
             return false;
         }