diff --git a/lib/privatekey.js b/lib/privatekey.js
index e80150462..26c31eb59 100644
--- a/lib/privatekey.js
+++ b/lib/privatekey.js
@@ -302,6 +302,9 @@ PrivateKey.getValidationError = function(data, network) {
  * @returns {Boolean} If the private key is would be valid
  */
 PrivateKey.isValid = function(data, network){
+  if (!data) {
+    return false;
+  }
   return !PrivateKey.getValidationError(data, network);
 };
 
diff --git a/test/privatekey.js b/test/privatekey.js
index c701983a7..5d072d171 100644
--- a/test/privatekey.js
+++ b/test/privatekey.js
@@ -267,6 +267,10 @@ describe('PrivateKey', function() {
       a.should.equal(false);
     });
 
+    it('should recognize that undefined is an invalid private key', function() {
+      PrivateKey.isValid().should.equal(false);
+    });
+
     it('should validate as true', function() {
       var a = PrivateKey.isValid('L3T1s1TYP9oyhHpXgkyLoJFGniEgkv2Jhi138d7R2yJ9F4QdDU2m');
       a.should.equal(true);