Index: Lib/test/test_multiprocessing.py
===================================================================
--- Lib/test/test_multiprocessing.py	(revision 69621)
+++ Lib/test/test_multiprocessing.py	(working copy)
@@ -547,6 +547,10 @@
         self.assertEqual(lock.release(), None)
         self.assertEqual(lock.release(), None)
         self.assertRaises((AssertionError, RuntimeError), lock.release)
+        
+    def test_lock_context(self):
+        with self.Lock():
+            pass
 
 
 class _TestSemaphore(BaseTestCase):
Index: Modules/_multiprocessing/semaphore.c
===================================================================
--- Modules/_multiprocessing/semaphore.c	(revision 69621)
+++ Modules/_multiprocessing/semaphore.c	(working copy)
@@ -546,7 +546,7 @@
 	 "acquire the semaphore/lock"},
 	{"release", (PyCFunction)semlock_release, METH_NOARGS, 
 	 "release the semaphore/lock"},
-	{"__enter__", (PyCFunction)semlock_acquire, METH_VARARGS,
+	{"__enter__", (PyCFunction)semlock_acquire, METH_VARARGS | METH_KEYWORDS,
 	 "enter the semaphore/lock"},
 	{"__exit__", (PyCFunction)semlock_release, METH_VARARGS, 
 	 "exit the semaphore/lock"},