diff --git a/Lib/gzip.py b/Lib/gzip.py
index 8002b43..ee0cbed 100644
--- a/Lib/gzip.py
+++ b/Lib/gzip.py
@@ -583,7 +583,7 @@ def main():
                 g = sys.stdout.buffer
             else:
                 if arg[-3:] != ".gz":
-                    sys.exit("filename doesn't end in .gz:", repr(arg))
+                    sys.exit(f"filename doesn't end in .gz: {arg!r}")
                 f = open(arg, "rb")
                 g = builtins.open(arg[:-3], "wb")
         else:
diff --git a/Lib/test/test_gzip.py b/Lib/test/test_gzip.py
index 1bb8f7a..1dcfa2b 100644
--- a/Lib/test/test_gzip.py
+++ b/Lib/test/test_gzip.py
@@ -775,7 +775,7 @@ def test_decompress_infile_outfile(self):
 
     def test_decompress_infile_outfile_error(self):
         rc, out, err = assert_python_failure('-m', 'gzip', '-d', 'thisisatest.out')
-        self.assertIn(b"filename doesn't end in .gz:", err)
+        self.assertEqual(b"filename doesn't end in .gz: 'thisisatest.out'", err.strip())
         self.assertEqual(rc, 1)
         self.assertEqual(out, b'')