diff --git a/lib/ace/test/asyncjs/assert.js b/lib/ace/test/asyncjs/assert.js
index 0972a8d1..198da4b2 100644
--- a/lib/ace/test/asyncjs/assert.js
+++ b/lib/ace/test/asyncjs/assert.js
@@ -53,14 +53,21 @@ assert.AssertionError = function AssertionError(options) {
 };
 oop.inherits(assert.AssertionError, Error);
 
+toJSON = function(obj) {
+    if (typeof JSON !== "undefined")
+        return JSON.stringify(obj);
+    else
+        return obj.toString();
+}
+
 assert.AssertionError.prototype.toString = function() {
   if (this.message) {
     return [this.name + ':', this.message].join(' ');
   } else {
     return [this.name + ':',
-            JSON.stringify(this.expected),
+            toJSON(this.expected),
             this.operator,
-            JSON.stringify(this.actual)].join(' ');
+            toJSON(this.actual)].join(' ');
   }
 };