diff --git a/peg.js b/peg.js
index 89e5341..44226a9 100644
--- a/peg.js
+++ b/peg.js
@@ -69,13 +69,15 @@ Peg.Use = function (getPattern) {
  * @return {Peg.Pattern<RegExpExecArray>}
  */
 Peg.Regex = function (regex) {
-  return Peg.WrapPattern(function (source, index) {
+  /** @type {Peg.Pattern<RegExpExecArray>} */
+  const pattern = Peg.WrapPattern(function (source, index) {
     regex.lastIndex = index;
     const matches = regex.exec(source);
     return matches
       ? [true, matches, regex.lastIndex]
-      : [false, index, regex.source];
+      : [false, index, pattern.expectLabel];
   }).expects(regex.source);
+  return pattern;
 };
 
 /**