diff --git a/lib/runner.js b/lib/runner.js
index 67e6fbabdb..cceacc9533 100644
--- a/lib/runner.js
+++ b/lib/runner.js
@@ -231,15 +231,7 @@ Runner.prototype.fail = function(test, err) {
   ++this.failures;
   test.state = 'failed';
 
-  if (!(err instanceof Error || (err && typeof err.message === 'string'))) {
-    err = new Error(
-      'the ' +
-        type(err) +
-        ' ' +
-        stringify(err) +
-        ' was thrown, throw an Error :)'
-    );
-  }
+  err = string2Error(err);
 
   try {
     err.stack =
@@ -731,6 +723,7 @@ Runner.prototype.uncaught = function(err) {
     debug('uncaught undefined exception');
     err = undefinedError();
   }
+  err = string2Error(err);
   err.uncaught = true;
 
   var runnable = this.currentRunnable;
@@ -993,6 +986,27 @@ function filterLeaks(ok, globals) {
   });
 }
 
+/**
+ *
+ * Check that the given object is an Error, convert it at such on the contrary
+ *
+ * @api private
+ * @param {Object} err
+ * @return {Error}
+ */
+function string2Error(err) {
+  if (!(err instanceof Error || (err && typeof err.message === 'string'))) {
+    err = new Error(
+      'the ' +
+        type(err) +
+        ' ' +
+        stringify(err) +
+        ' was thrown, throw an Error :)'
+    );
+  }
+  return err;
+}
+
 /**
  * Array of globals dependent on the environment.
  *
diff --git a/test/unit/throw.spec.js b/test/unit/throw.spec.js
index 6aca25750c..b9f520178b 100644
--- a/test/unit/throw.spec.js
+++ b/test/unit/throw.spec.js
@@ -26,6 +26,24 @@ describe('a test that throws', function() {
     });
   });
 
+  describe('non-extensible', function() {
+    it('should not crash if throwing non-extensible type', function(done) {
+      var test = new Test('im async and throw string async', function(done2) {
+        process.nextTick(function() {
+          throw 'error';
+        });
+      });
+      suite.addTest(test);
+      runner = new Runner(suite);
+      runner.on('end', function() {
+        expect(runner.failures, 'to be', 1);
+        expect(test.state, 'to be', 'failed');
+        done();
+      });
+      runner.run();
+    });
+  });
+
   describe('undefined', function() {
     it('should not pass if throwing sync and test is sync', function(done) {
       var test = new Test('im sync and throw undefined sync', function() {