diff --git a/tests/test_main.py b/tests/test_main.py
index 95405b0d..e4c5f0e8 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -734,7 +734,7 @@ THIS FILE IS INVALID
         resources / 'ccitt.pdf', outdir / 'out.pdf',
         '--pdf-renderer', renderer,
         '--tesseract-config', cfg_file)
-    assert "parameter not found" in err, "No error message"
+    assert "parameter not found" in err.lower(), "No error message"
     assert p.returncode == ExitCode.invalid_config