diff --git a/src/raven.js b/src/raven.js
index 9235ed926f18..0fc03711d474 100644
--- a/src/raven.js
+++ b/src/raven.js
@@ -424,7 +424,7 @@ function isFunction(what) {
 }
 
 function isString(what) {
-    return typeof what === 'string';
+    return objectPrototype.toString.call(what) === '[object String]';
 }
 
 function isObject(what) {
diff --git a/test/raven.test.js b/test/raven.test.js
index a40821ed7af1..3a6c4464503f 100644
--- a/test/raven.test.js
+++ b/test/raven.test.js
@@ -209,6 +209,8 @@ describe('globals', function() {
     describe('isString', function() {
         it('should do as advertised', function() {
             assert.isTrue(isString(''));
+            assert.isTrue(isString(String('')));
+            assert.isTrue(isString(new String('')));
             assert.isFalse(isString({}));
             assert.isFalse(isString(undefined));
             assert.isFalse(isString(function(){}));