diff --git a/lib/hdprivatekey.js b/lib/hdprivatekey.js
index 8e40411..a5db864 100644
--- a/lib/hdprivatekey.js
+++ b/lib/hdprivatekey.js
@@ -106,8 +106,13 @@ HDPrivateKey._getDerivationIndexes = function(path) {
   }
 
   var indexes = steps.slice(1).map(function(step) {
-    var index = parseInt(step);
-    index += step != index.toString() ? HDPrivateKey.Hardened : 0;
+    var index = step ? +step : NaN;
+
+    var isHardened = isNaN(index) && step[step.length-1] == "'";
+    if (isHardened) {
+      index = (+(step.slice(0, -1))) + HDPrivateKey.Hardened;
+    }
+
     return index;
   });
 
diff --git a/test/hdprivatekey.js b/test/hdprivatekey.js
index e6c57e8..0888007 100644
--- a/test/hdprivatekey.js
+++ b/test/hdprivatekey.js
@@ -234,6 +234,9 @@ describe('HDPrivate key interface', function() {
       valid = HDPrivateKey.isValidPath('m/');
       valid.should.equal(false);
 
+      valid = HDPrivateKey.isValidPath('m/12asd');
+      valid.should.equal(false);
+
       valid = HDPrivateKey.isValidPath(HDPrivateKey.MaxHardened);
       valid.should.equal(false);
     });
@@ -259,6 +262,15 @@ describe('HDPrivate key interface', function() {
 
       indexes = HDPrivateKey._getDerivationIndexes("bad path");
       expect(indexes).to.be.null;
+
+      indexes = HDPrivateKey._getDerivationIndexes("K");
+      expect(indexes).to.be.null;
+
+      indexes = HDPrivateKey._getDerivationIndexes("m/");
+      expect(indexes).to.be.null;
+
+      indexes = HDPrivateKey._getDerivationIndexes("m/123asd");
+      expect(indexes).to.be.null;
     });
   });