diff --git a/Doc/library/hashlib.rst b/Doc/library/hashlib.rst
index 955afb8..36f386c 100644
--- a/Doc/library/hashlib.rst
+++ b/Doc/library/hashlib.rst
@@ -105,6 +105,12 @@
    concatenation of all the arguments: ``m.update(a); m.update(b)`` is
    equivalent to ``m.update(a+b)``.
 
+   .. versionchanged:: 2.7
+
+      The Python GIL is released to allow other threads to run while
+      hash updates on data larger than 2048 bytes is taking place when
+      using hash algorithms supplied by OpenSSL.
+
 
 .. method:: hash.digest()
 
diff --git a/Lib/test/test_hashlib.py b/Lib/test/test_hashlib.py
index 9b51459..594f5dd 100644
--- a/Lib/test/test_hashlib.py
+++ b/Lib/test/test_hashlib.py
@@ -2,11 +2,16 @@
 #
 # $Id$
 #
-#  Copyright (C) 2005   Gregory P. Smith (greg@krypto.org)
+#  Copyright (C) 2005-2009   Gregory P. Smith (greg@krypto.org)
 #  Licensed to PSF under a Contributor Agreement.
 #
 
 import hashlib
+from io import StringIO
+try:
+    import threading
+except ImportError:
+    threading = None
 import unittest
 from test import support
 from test.support import _4G, precisionbigmemtest
@@ -224,6 +229,45 @@
         m = hashlib.md5(b'x' * gil_minsize)
         self.assertEquals(m.hexdigest(), 'cfb767f225d58469c5de3632a8803958')
 
+    def test_threaded_hashing(self):
+        if not threading:
+            raise unittest.SkipTest('No threading module.')
+
+        # Updating the same hash object from several threads at once
+        # using data chunk sizes containing the same byte sequences.
+        #
+        # If the internal locks are working to prevent multiple
+        # updates on the same object from running at once, the resulting
+        # hash will be the same as doing it single threaded upfront.
+        hasher = hashlib.sha1()
+        num_threads = 5
+        smallest_data = b'swineflu'
+        data = smallest_data*200000
+        expected_hash = hashlib.sha1(data*num_threads).hexdigest()
+
+        def hash_in_chunks(chunk_size, event):
+            index = 0
+            while index < len(data):
+                hasher.update(data[index:index+chunk_size])
+                index += chunk_size
+            event.set()
+
+        events = []
+        for threadnum in range(num_threads):
+            chunk_size = len(data) // (10**threadnum)
+            assert chunk_size > 0
+            assert chunk_size % len(smallest_data) == 0
+            event = threading.Event()
+            events.append(event)
+            threading.Thread(target=hash_in_chunks,
+                             args=(chunk_size, event)).start()
+
+        for event in events:
+            event.wait()
+
+        self.assertEqual(expected_hash, hasher.hexdigest())
+
+
 def test_main():
     support.run_unittest(HashLibTestCase)
 
diff --git a/Modules/_hashopenssl.c b/Modules/_hashopenssl.c
index 569d441..0dae515 100644
--- a/Modules/_hashopenssl.c
+++ b/Modules/_hashopenssl.c
@@ -1,7 +1,7 @@
 /* Module that wraps all OpenSSL hash algorithms */
 
 /*
- * Copyright (C) 2005-2007   Gregory P. Smith (greg@krypto.org)
+ * Copyright (C) 2005-2009   Gregory P. Smith (greg@krypto.org)
  * Licensed to PSF under a Contributor Agreement.
  *
  * Derived from a skeleton of shamodule.c containing work performed by:
@@ -17,21 +17,8 @@
 #include "structmember.h"
 #include "hashlib.h"
 
-/* EVP is the preferred interface to hashing in OpenSSL */
-#include <openssl/evp.h>
-
-#define MUNCH_SIZE INT_MAX
-
-
-#ifndef HASH_OBJ_CONSTRUCTOR
-#define HASH_OBJ_CONSTRUCTOR 0
-#endif
-
-#define HASHLIB_GIL_MINSIZE 2048
-
 #ifdef WITH_THREAD
-    #include "pythread.h"
-
+#include "pythread.h"
     #define ENTER_HASHLIB(obj) \
         if ((obj)->lock) { \
             if (!PyThread_acquire_lock((obj)->lock, 0)) { \
@@ -49,6 +36,20 @@
     #define LEAVE_HASHLIB(obj)
 #endif
 
+/* EVP is the preferred interface to hashing in OpenSSL */
+#include <openssl/evp.h>
+
+#define MUNCH_SIZE INT_MAX
+
+/* TODO(gps): We should probably make this a module or EVPobject attribute
+ * to allow the user to optimize based on the platform they're using. */
+#define HASHLIB_GIL_MINSIZE 2048
+
+#ifndef HASH_OBJ_CONSTRUCTOR
+#define HASH_OBJ_CONSTRUCTOR 0
+#endif
+
+
 typedef struct {
     PyObject_HEAD
     PyObject            *name;  /* name of this hash algorithm */
@@ -122,11 +123,18 @@
     PyObject_Del(self);
 }
 
+static void locked_EVP_MD_CTX_copy(EVP_MD_CTX *new_ctx_p, EVPobject *self)
+{
+    ENTER_HASHLIB(self);
+    EVP_MD_CTX_copy(new_ctx_p, &self->ctx);
+    LEAVE_HASHLIB(self);
+}
 
 /* External methods for a hash object */
 
 PyDoc_STRVAR(EVP_copy__doc__, "Return a copy of the hash object.");
 
+
 static PyObject *
 EVP_copy(EVPobject *self, PyObject *unused)
 {
@@ -135,9 +143,7 @@
     if ( (newobj = newEVPobject(self->name))==NULL)
         return NULL;
 
-    ENTER_HASHLIB(self);
-    EVP_MD_CTX_copy(&newobj->ctx, &self->ctx);
-    LEAVE_HASHLIB(self);
+    locked_EVP_MD_CTX_copy(&newobj->ctx, self);
     return (PyObject *)newobj;
 }
 
@@ -152,9 +158,7 @@
     PyObject *retval;
     unsigned int digest_size;
 
-    ENTER_HASHLIB(self);
-    EVP_MD_CTX_copy(&temp_ctx, &self->ctx);
-    LEAVE_HASHLIB(self);
+    locked_EVP_MD_CTX_copy(&temp_ctx, self);
     digest_size = EVP_MD_CTX_size(&temp_ctx);
     EVP_DigestFinal(&temp_ctx, digest, NULL);
 
@@ -176,9 +180,7 @@
     unsigned int i, j, digest_size;
 
     /* Get the raw (binary) digest value */
-    ENTER_HASHLIB(self);
-    EVP_MD_CTX_copy(&temp_ctx, &self->ctx);
-    LEAVE_HASHLIB(self);
+    locked_EVP_MD_CTX_copy(&temp_ctx, self);
     digest_size = EVP_MD_CTX_size(&temp_ctx);
     EVP_DigestFinal(&temp_ctx, digest, NULL);
 
@@ -221,11 +223,7 @@
 #ifdef WITH_THREAD
     if (self->lock == NULL && view.len >= HASHLIB_GIL_MINSIZE) {
         self->lock = PyThread_allocate_lock();
-        if (self->lock == NULL) {
-            PyBuffer_Release(&view);
-            PyErr_SetString(PyExc_MemoryError, "unable to allocate lock");
-            return NULL;
-        }
+        /* fail? lock = NULL and we fail over to non-threaded code. */
     }
 
     if (self->lock != NULL) {
@@ -257,9 +255,7 @@
 EVP_get_block_size(EVPobject *self, void *closure)
 {
     long block_size;
-    ENTER_HASHLIB(self);
     block_size = EVP_MD_CTX_block_size(&self->ctx);
-    LEAVE_HASHLIB(self);
     return PyLong_FromLong(block_size);
 }
 
@@ -267,9 +263,7 @@
 EVP_get_digest_size(EVPobject *self, void *closure)
 {
     long size;
-    ENTER_HASHLIB(self);
     size = EVP_MD_CTX_size(&self->ctx);
-    LEAVE_HASHLIB(self);
     return PyLong_FromLong(size);
 }