diff --git a/Lib/test/test_multiprocessing.py b/Lib/test/test_multiprocessing.py
index d2503f6..29323a5 100644
--- a/Lib/test/test_multiprocessing.py
+++ b/Lib/test/test_multiprocessing.py
@@ -548,6 +548,10 @@
         self.assertEqual(lock.release(), None)
         self.assertRaises((AssertionError, RuntimeError), lock.release)
 
+    def test_lock_context(self):
+        with self.Lock():
+            pass
+
 
 class _TestSemaphore(BaseTestCase):
 
diff --git a/Misc/ACKS b/Misc/ACKS
index a869119..d902c13 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -251,6 +251,7 @@
 Jonathan Giddy
 Johannes Gijsbers
 Michael Gilfix
+Tim Golden
 Chris Gonnerman
 David Goodger
 Hans de Graaff
diff --git a/Misc/NEWS b/Misc/NEWS
index f882ed9..d49fc0d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -92,6 +92,9 @@
 Library
 -------
 
+- Issue #5261: Patch multiprocessing's semaphore.c to support context
+  manager use: "with multiprocessing.Lock()" works now.
+
 - Issue #5177: Multiprocessing's SocketListener class now uses 
   socket.SO_REUSEADDR on all connections so that the user no longer needs
   to wait 120 seconds for the socket to expire.
diff --git a/Modules/_multiprocessing/semaphore.c b/Modules/_multiprocessing/semaphore.c
index a5ba71e..2c2fb10f 100644
--- a/Modules/_multiprocessing/semaphore.c
+++ b/Modules/_multiprocessing/semaphore.c
@@ -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"},