diff --git a/apiclient/ext/file.py b/apiclient/ext/file.py
index dba723e..a243fd2 100644
--- a/apiclient/ext/file.py
+++ b/apiclient/ext/file.py
@@ -8,6 +8,7 @@
 __author__ = 'jcgregorio@google.com (Joe Gregorio)'
 
 import pickle
+import threading
 
 from apiclient.oauth import Storage as BaseStorage
 
@@ -17,6 +18,7 @@
 
   def __init__(self, filename):
     self._filename = filename
+    self._lock = threading.Lock()
 
   def get(self):
     """Retrieve Credential from file.
@@ -24,6 +26,7 @@
     Returns:
       apiclient.oauth.Credentials
     """
+    self._lock.acquire()
     try:
       f = open(self._filename, 'r')
       credentials = pickle.loads(f.read())
@@ -31,6 +34,7 @@
       credentials.set_store(self.put)
     except:
       credentials = None
+    self._lock.release()
 
     return credentials
 
@@ -40,6 +44,8 @@
     Args:
       credentials: Credentials, the credentials to store.
     """
+    self._lock.acquire()
     f = open(self._filename, 'w')
     f.write(pickle.dumps(credentials))
     f.close()
+    self._lock.release()