diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-09-12-16-36-16.bpo-38106.4pApn7.rst b/Misc/NEWS.d/next/Core and Builtins/2019-09-12-16-36-16.bpo-38106.4pApn7.rst
new file mode 100644
index 00000000000..b2b80ceece8
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2019-09-12-16-36-16.bpo-38106.4pApn7.rst	
@@ -0,0 +1,5 @@
+Fix race in PyThread_release_lock that was leading to memory corruption and
+deadlocks. The fix applies to POSIX systems where Python locks are implemented
+with mutex and condition variable because POSIX semaphores are either not
+provided, or are known to be broken. One particular example of such system is
+macOS.
diff --git a/Python/thread_pthread.h b/Python/thread_pthread.h
index 6d4b3b389f8..4d792a123a7 100644
--- a/Python/thread_pthread.h
+++ b/Python/thread_pthread.h
@@ -430,12 +430,15 @@ PyThread_free_lock(PyThread_type_lock lock)
     (void) error; /* silence unused-but-set-variable warning */
     dprintf(("PyThread_free_lock(%p) called\n", lock));
 
-    status = pthread_mutex_destroy( &thelock->mut );
-    CHECK_STATUS("pthread_mutex_destroy");
-
+    /* some pthread-like implementations tie the mutex to the cond
+     * and must have the cond destroyed first.
+     */
     status = pthread_cond_destroy( &thelock->lock_released );
     CHECK_STATUS("pthread_cond_destroy");
 
+    status = pthread_mutex_destroy( &thelock->mut );
+    CHECK_STATUS("pthread_mutex_destroy");
+
     free((void *)thelock);
 }
 
@@ -497,12 +500,12 @@ PyThread_release_lock(PyThread_type_lock lock)
 
     thelock->locked = 0;
 
-    status = pthread_mutex_unlock( &thelock->mut );
-    CHECK_STATUS("pthread_mutex_unlock[3]");
-
     /* wake up someone (anyone, if any) waiting on the lock */
     status = pthread_cond_signal( &thelock->lock_released );
     CHECK_STATUS("pthread_cond_signal");
+
+    status = pthread_mutex_unlock( &thelock->mut );
+    CHECK_STATUS("pthread_mutex_unlock[3]");
 }
 
 #endif /* USE_SEMAPHORES */