1 files changed, 5 insertions, 4 deletions
diff --git a/Lib/test/libregrtest/setup.py b/Lib/test/libregrtest/setup.py
index b79175944d..0bfd644bb3 100644
--- a/Lib/test/libregrtest/setup.py
+++ b/Lib/test/libregrtest/setup.py
@@ -5,6 +5,7 @@ import signal
 import sys
 import unittest
 from test import support
+from test.support.os_helper import TESTFN_UNDECODABLE, FS_NONASCII
 try:
     import gc
 except ImportError:
@@ -105,10 +106,10 @@ def setup_tests(ns):
 
     # Ensure there's a non-ASCII character in env vars at all times to force
     # tests consider this case. See BPO-44647 for details.
-    os.environ.setdefault(
-        UNICODE_GUARD_ENV,
-        "\N{SMILING FACE WITH SUNGLASSES}",
-    )
+    if TESTFN_UNDECODABLE and os.supports_bytes_environ:
+        os.environb.setdefault(UNICODE_GUARD_ENV.encode(), TESTFN_UNDECODABLE)
+    elif FS_NONASCII:
+        os.environ.setdefault(UNICODE_GUARD_ENV, FS_NONASCII)
 
 
 def replace_stdout():