diff --git a/lib/utils.js b/lib/utils.js
index 3650a707cc..7e44edf28a 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -444,7 +444,10 @@ function jsonStringify(object, spaces, depth) {
           : val.toString();
         break;
       case 'date':
-        val = '[Date: ' + val.toISOString() + ']';
+        var sDate = isNaN(val.getTime())        // Invalid date
+          ? val.toString()
+          : val.toISOString();
+        val = '[Date: ' + sDate + ']';
         break;
       case 'buffer':
         var json = val.toJSON();
diff --git a/test/acceptance/utils.js b/test/acceptance/utils.js
index 6b373a45e3..e67250b6d1 100644
--- a/test/acceptance/utils.js
+++ b/test/acceptance/utils.js
@@ -89,6 +89,10 @@ describe('lib/utils', function () {
       stringify(date).should.equal('[Date: ' + date.toISOString() + ']');
     });
 
+    it('should return invalid Date object with .toString() + string prefix', function() {
+      stringify(new Date('')).should.equal('[Date: ' + new Date('').toString() + ']');
+    });
+
     describe('#Number', function() {
       it('should show the handle -0 situations', function() {
         stringify(-0).should.eql('-0');