diff --git a/Misc/NEWS b/Misc/NEWS
index 1d6f5c36401..94db851d1e5 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -23,6 +23,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #27533: Release GIL in nt._isdir
+
 - Issue #17711: Fixed unpickling by the persistent ID with protocol 0.
   Original patch by Alexandre Vassalotti.
 
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 7f16a83e788..424daac99ee 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -3893,10 +3893,12 @@ os__isdir_impl(PyObject *module, path_t *path)
 {
     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;