diff --git a/beaker/session.py b/beaker/session.py
index e14a6bb1..e9b9b4b0 100644
--- a/beaker/session.py
+++ b/beaker/session.py
@@ -2,6 +2,7 @@
 import os
 from datetime import datetime, timedelta
 import time
+from re import match
 from beaker.crypto import hmac as HMAC, hmac_sha1 as SHA1, sha1
 from beaker import crypto, util
 from beaker.cache import clsmap
@@ -153,6 +154,9 @@ def __init__(self, request, id=None, invalidate_corrupt=False,
             if not self.id and self.key in self.cookie:
                 self.id = self.cookie[self.key].value
 
+            if self.id and not match("^[0-9a-zA-Z-_]+\Z", self.id):
+                self.id = None
+
         self.is_new = self.id is None
         if self.is_new:
             self._create_id()
diff --git a/tests/test_cookie_traversal.py b/tests/test_cookie_traversal.py
new file mode 100644
index 00000000..565c2099
--- /dev/null
+++ b/tests/test_cookie_traversal.py
@@ -0,0 +1,42 @@
+# -*- coding: utf-8 -*-
+import sys
+import time
+import warnings
+import os
+
+from beaker.session import Session
+
+
+def get_session(**kwargs):
+    """A shortcut for creating :class:`Session` instance"""
+    options = {}
+    options.update(**kwargs)
+    return Session({}, **options)
+
+def test_file_traversal_cookie():
+    session = get_session(id='..traversed', type='file', data_dir='.')
+    session[u'traversal'] = u'True'
+    session.save()
+    assert not os.path.exists('./..traversed.cache') 
+
+
+def test_save_load():
+    """Test if the data is actually persistent across requests"""
+    session = get_session(type='file', data_dir='.')
+    session[u'Suomi'] = u'Kimi Räikkönen'
+    session[u'Great Britain'] = u'Jenson Button'
+    session[u'Deutchland'] = u'Sebastian Vettel'
+    session.save()
+
+    session = get_session(id=session.id, type='file', data_dir='.')
+    assert u'Suomi' in session
+    assert u'Great Britain' in session
+    assert u'Deutchland' in session
+
+    assert session[u'Suomi'] == u'Kimi Räikkönen'
+    assert session[u'Great Britain'] == u'Jenson Button'
+    assert session[u'Deutchland'] == u'Sebastian Vettel'
+
+test_save_load()
+test_file_traversal_cookie()
+