diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -6650,7 +6650,7 @@ posix_confstr(PyObject *self, PyObject *
             }
         }
         else {
-            result = PyUnicode_FromStringAndSize(recvbuf, len - 1);
+            result = PyUnicode_DecodeFSDefaultAndSize(recvbuf, len - 1);
         }
     }
 finally: