diff -r 49e1e8413ecc Modules/posixmodule.c
--- a/Modules/posixmodule.c	Sat Jul 16 10:46:10 2016 -0700
+++ b/Modules/posixmodule.c	Sat Jul 16 13:08:43 2016 -0700
@@ -3893,10 +3893,12 @@
 {
     DWORD attributes;
 
+    Py_BEGIN_ALLOW_THREADS
     if (!path->narrow)
         attributes = GetFileAttributesW(path->wide);
     else
         attributes = GetFileAttributesA(path->narrow);
+    Py_END_ALLOW_THREADS
 
     if (attributes == INVALID_FILE_ATTRIBUTES)
         Py_RETURN_FALSE;