diff --git a/Lib/test/test_clinic.py b/Lib/test/test_clinic.py
index 32c4b1e67f9574..1c01fb0ed36888 100644
--- a/Lib/test/test_clinic.py
+++ b/Lib/test/test_clinic.py
@@ -1306,7 +1306,7 @@ 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.