diff --git a/lib/mocha.js b/lib/mocha.js
index cce2bb9b2f..66adf6423d 100644
--- a/lib/mocha.js
+++ b/lib/mocha.js
@@ -781,10 +781,11 @@ Mocha.prototype.run = function(fn) {
   exports.reporters.Base.hideDiff = options.hideDiff;
 
   function done(failures) {
+    fn = fn || function fn() {};
     if (reporter.done) {
       reporter.done(failures, fn);
     } else {
-      fn && fn(failures);
+      fn(failures);
     }
   }
 
diff --git a/test/unit/mocha.spec.js b/test/unit/mocha.spec.js
index 2511b1204d..00a5f8eac0 100644
--- a/test/unit/mocha.spec.js
+++ b/test/unit/mocha.spec.js
@@ -56,6 +56,20 @@ describe('Mocha', function() {
     });
   });
 
+  describe('.reporter("xunit").run(fn)', function() {
+    it('should not raise errors if callback was not provided', function() {
+      var mocha = new Mocha();
+      expect(function() {
+        try {
+          mocha.reporter('xunit').run();
+        } catch (e) {
+          console.log(e);
+          expect.fail(e.message);
+        }
+      }, 'not to throw');
+    });
+  });
+
   describe('.addFile()', function() {
     it('should add the given file to the files array', function() {
       var mocha = new Mocha(opts);