diff --git a/lib/util/named-group-regexp.js b/lib/util/named-group-regexp.js
index 21cb03f..3eaeb78 100644
--- a/lib/util/named-group-regexp.js
+++ b/lib/util/named-group-regexp.js
@@ -14,7 +14,7 @@ const pattern = [
 	'[>\']',
 	// Get everything up to the end of the capture group: this is the RegExp used
 	// when matching URLs to this route, which we can use for validation purposes.
-	'([^\\)]*(\))?)\??)',
+	'([^\\)]*(\\))?)\\??',
 	// Capture group end
 	'\\)',
 ].join( '' );