diff --git a/lib/async.js b/lib/async.js
index bbb349572..1e76ee8bc 100644
--- a/lib/async.js
+++ b/lib/async.js
@@ -112,11 +112,18 @@
     //// exported async module functions ////
 
     //// nextTick implementation with browser-compatible fallback ////
+
+    // capture the global reference to guard against fakeTimer mocks
+    var _setImmediate;
+    if (typeof setImmediate === 'function') {
+        _setImmediate = setImmediate;
+    }
+
     if (typeof process === 'undefined' || !(process.nextTick)) {
-        if (typeof setImmediate === 'function') {
+        if (_setImmediate) {
             async.nextTick = function (fn) {
                 // not a direct alias for IE10 compatibility
-                setImmediate(fn);
+                _setImmediate(fn);
             };
             async.setImmediate = async.nextTick;
         }
@@ -129,10 +136,10 @@
     }
     else {
         async.nextTick = process.nextTick;
-        if (typeof setImmediate !== 'undefined') {
+        if (_setImmediate) {
             async.setImmediate = function (fn) {
               // not a direct alias for IE10 compatibility
-              setImmediate(fn);
+              _setImmediate(fn);
             };
         }
         else {