diff --git a/lib/persistent_session.js b/lib/persistent_session.js
index cabcfa6..7c45edc 100644
--- a/lib/persistent_session.js
+++ b/lib/persistent_session.js
@@ -394,8 +394,10 @@ PersistentSession.prototype.clear = function _psClear(key, list) {
     self.set(akey, undefined, false, false);
 
     changed(self._dict.keyDeps[akey]);
-    changed(self._dict.keyValueDeps[akey][value]);
-    changed(self._dict.keyValueDeps[akey]['undefined']);
+    if (self._dict.keyValueDeps[akey]) {
+      changed(self._dict.keyValueDeps[akey][value]);
+      changed(self._dict.keyValueDeps[akey]['undefined']);
+    }
 
     delete self._dict.keys[akey]; // remove the key
   });
diff --git a/tests/client/persistent_session.js b/tests/client/persistent_session.js
index fa93f23..dc4fdcb 100644
--- a/tests/client/persistent_session.js
+++ b/tests/client/persistent_session.js
@@ -36,6 +36,19 @@ Tinytest.add("clear all keys", function(test) {
   test.equal(undefined, result);
 });
 
+Tinytest.add("skip undefined keys", function(test) {
+  var TestSession = new PersistentSession(Random.id());
+  test.equal(_.keys(TestSession._dict.keys).length, 0);
+
+  TestSession.set(undefined, 'woo');
+  test.equal(_.keys(TestSession._dict.keys).length, 1);
+
+  TestSession.clear();
+
+  test.equal(_.keys(TestSession._dict.keys).length, 0);
+
+});
+
 Tinytest.add("clear single key", function(test) {
   var TestSession = new PersistentSession(Random.id());