diff -r 345ec7455b75 Modules/posixmodule.c
--- a/Modules/posixmodule.c	Thu Jul 14 22:00:03 2016 -0700
+++ b/Modules/posixmodule.c	Sat Jul 16 15:38:53 2016 -0700
@@ -4444,7 +4444,9 @@
                           Py_FileSystemDefaultEncoding, &path))
         return NULL;
 
+    Py_BEGIN_ALLOW_THREADS
     attributes = GetFileAttributesA(path);
+    Py_END_ALLOW_THREADS
     PyMem_Free(path);
     if (attributes == INVALID_FILE_ATTRIBUTES)
         Py_RETURN_FALSE;