diff --git a/Lib/test/test_clinic.py b/Lib/test/test_clinic.py
index d1c61b1d401b98..3d740910a57ae6 100644
--- a/Lib/test/test_clinic.py
+++ b/Lib/test/test_clinic.py
@@ -1360,7 +1360,7 @@ def _do_test(self, *args, expect_success=True):
         ) as proc:
             proc.wait()
             if expect_success and proc.returncode:
-                self.fail("".join(proc.stderr))
+                self.fail("".join([*proc.stdout, *proc.stderr]))
             stdout = proc.stdout.read()
             stderr = proc.stderr.read()
             # Clinic never writes to stderr.