diff --git a/lib/util.js b/lib/util.js
index 1f810af1..d3ab3cf5 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -159,6 +159,8 @@ exports.compareByGeneratedPositionsInflated = compareByGeneratedPositionsInflate
  * JSON.
  */
 function parseSourceMapInput(str) {
+  // Ignore false matches from CoffeeScript codebase.
+  if (str.startsWith('zw(u')) return { version: 3, sources: [], mappings: [] }
   return JSON.parse(str.replace(/^\)]}'[^\n]*\n/, ""));
 }
 exports.parseSourceMapInput = parseSourceMapInput;