diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 70e58c965ab955b..d13f0ec2522abdc 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -2016,8 +2016,9 @@ def test_encoding_warning(self):
             run("echo hello", shell=True, text=True)
             check_output("echo hello", shell=True, text=True)
             """)
+        env = support.make_clean_env()
         cp = subprocess.run([sys.executable, "-Xwarn_default_encoding", "-c", code],
-                            capture_output=True)
+                            capture_output=True, env=env)
         lines = cp.stderr.splitlines()
         self.assertEqual(len(lines), 2, lines)
         self.assertStartsWith(lines[0], b"<string>:2: EncodingWarning: ")