diff --git a/lib/util.js b/lib/util.js
index b2bfa7c5ddd56b..2dc2259338f9a3 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -81,7 +81,8 @@ exports.debuglog = function(set) {
     debugEnviron = process.env.NODE_DEBUG || '';
   set = set.toUpperCase();
   if (!debugs[set]) {
-    if (new RegExp('\\b' + set + '\\b', 'i').test(debugEnviron)) {
+    if (isFunction(RegExp) &&
+        new RegExp('\\b' + set + '\\b', 'i').test(debugEnviron)) {
       var pid = process.pid;
       debugs[set] = function() {
         var msg = exports.format.apply(exports, arguments);