diff --git a/Lib/test/lock_tests.py b/Lib/test/lock_tests.py
--- a/Lib/test/lock_tests.py
+++ b/Lib/test/lock_tests.py
@@ -247,6 +247,7 @@ class RLockTests(BaseLockTests):
         # Cannot release an unacquired lock
         lock = self.locktype()
         self.assertRaises(RuntimeError, lock.release)
+        self.assertRaises(RuntimeError, lock._release_save)
         lock.acquire()
         lock.acquire()
         lock.release()
@@ -254,6 +255,7 @@ class RLockTests(BaseLockTests):
         lock.release()
         lock.release()
         self.assertRaises(RuntimeError, lock.release)
+        self.assertRaises(RuntimeError, lock._release_save)
 
     def test_different_thread(self):
         # Cannot release from a different thread
diff --git a/Lib/threading.py b/Lib/threading.py
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -156,6 +156,8 @@ class _RLock(_Verbose):
     def _release_save(self):
         if __debug__:
             self._note("%s._release_save()", self)
+        if self._count == 0:
+            raise RuntimeError("cannot release un-acquired lock")
         count = self._count
         self._count = 0
         owner = self._owner
diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -414,6 +414,12 @@ rlock_release_save(rlockobject *self)
     long owner;
     unsigned long count;
 
+    if (self->rlock_count == 0) {
+        PyErr_SetString(PyExc_RuntimeError,
+                        "cannot release un-acquired lock");
+        return NULL;
+    }
+
     owner = self->rlock_owner;
     count = self->rlock_count;
     self->rlock_count = 0;
@@ -1310,7 +1316,7 @@ PyInit__thread(void)
     d = PyModule_GetDict(m);
     ThreadError = PyExc_RuntimeError;
     Py_INCREF(ThreadError);
-    
+
     PyDict_SetItemString(d, "error", ThreadError);
     Locktype.tp_doc = lock_doc;
     Py_INCREF(&Locktype);