diff --git a/lodash/lodash-tests.ts b/lodash/lodash-tests.ts
index 38a296544..bf7f77431 100644
--- a/lodash/lodash-tests.ts
+++ b/lodash/lodash-tests.ts
@@ -625,6 +625,10 @@ result = <boolean>_.isFinite(Infinity);
 
 result = <boolean>_.isFunction(_);
 
+result = <boolean>_.isNaN(NaN);
+result = <boolean>_.isNaN(new Number(NaN));
+result = <boolean>_.isNaN(undefined);
+
 var mergeNames = {
   'stooges': [
     { 'name': 'moe' },
diff --git a/lodash/lodash.d.ts b/lodash/lodash.d.ts
index fd771b1ce..7b6792b45 100644
--- a/lodash/lodash.d.ts
+++ b/lodash/lodash.d.ts
@@ -2433,6 +2433,16 @@ declare module _ {
 	**/
 	export function isFunction(value: any): boolean;
 
+	/**
+	* Checks if value is NaN.
+	*
+	* Note: This is not the same as native isNaN which will return true for undefined and other 
+	* non-numeric values. See http://es5.github.io/#x15.1.2.4.
+	* @param value The value to check.
+	* @return True if the value is NaN, else false.
+	**/
+	export function isNaN(value: any): boolean;
+
 	/**
 	* Recursively merges own enumerable properties of the source object(s), that don't resolve 
 	* to undefined into the destination object. Subsequent sources will overwrite property 
@@ -2681,15 +2691,6 @@ declare module _ {
 	**/
 	export function isRegExp(object: any): boolean;
 
-	/**
-	* Returns true if object is NaN.
-	* Note: this is not the same as the native isNaN function,
-	* which will also return true if the variable is undefined.
-	* @param object Check if this object is NaN.
-	* @return True if `object` is NaN, otherwise false.
-	**/
-	export function isNaN(object: any): boolean;
-
 	/**
 	* Returns true if the value of object is null.
 	* @param object Check if this object is null.