diff --git a/lib/empower.js b/lib/empower.js
index c1b0002..5428629 100644
--- a/lib/empower.js
+++ b/lib/empower.js
@@ -14,18 +14,23 @@
  */
 (function (root, factory) {
     'use strict';
+    var isPhantom = (typeof root.callPhantom === 'function');
 
     // using returnExports UMD pattern
     if (typeof define === 'function' && define.amd) {
         define(factory);
     } else if (typeof exports === 'object') {
-        module.exports = factory();
+        module.exports = factory(isPhantom);
     } else {
-        root.empower = factory();
+        root.empower = factory(isPhantom);
     }
-}(this, function () {
+}(this, function (isPhantom) {
     'use strict';
 
+    // How to pass isPhantom to AMD define function in UMD style?
+    if (typeof define === 'function' && define.amd) {
+        isPhantom = (typeof window.callPhantom === 'function');
+    }
 
     function defaultOptions () {
         return {
@@ -105,6 +110,7 @@
     function enhance (target, formatter, config) {
         var eagerEvaluation = !(config.modifyMessageOnFail || config.saveContextOnFail),
             doPowerAssert = function (baseAssert, args, message, context) {
+                var f;
                 if (eagerEvaluation) {
                     args.push(buildPowerAssertText(message, context));
                     return baseAssert.apply(target, args);
@@ -116,16 +122,29 @@
                     if (e.name !== 'AssertionError') {
                         throw e;
                     }
+                    if (typeof target.AssertionError !== 'function') {
+                        throw e;
+                    }
+                    if (isPhantom) {
+                        f = new target.AssertionError({
+                            actual: e.actual,
+                            expected: e.expected,
+                            operator: e.operator,
+                            message: e.message
+                        });
+                    } else {
+                        f = e;
+                    }
                     if (config.modifyMessageOnFail) {
-                        e.message = buildPowerAssertText(message, context);
+                        f.message = buildPowerAssertText(message, context);
                         if (typeof e.generatedMessage !== 'undefined') {
-                            e.generatedMessage = false;
+                            f.generatedMessage = false;
                         }
                     }
                     if (config.saveContextOnFail) {
-                        e.powerAssertContext = context;
+                        f.powerAssertContext = context;
                     }
-                    throw e;
+                    throw f;
                 }
             },
             enhancement = (typeof target === 'function') ? decorateOneArg(target, target, doPowerAssert) : {},