diff --git a/tests/test_syntax.py b/tests/test_syntax.py
index da7c3715d..308636d80 100644
--- a/tests/test_syntax.py
+++ b/tests/test_syntax.py
@@ -333,6 +333,7 @@ def test_from_path_unknown_lexer():
     try:
         os.write(fh, b"import this\n")
         syntax = Syntax.from_path(path)
+        assert syntax.lexer is None
         assert syntax.code == "import this\n"
     finally:
         os.remove(path)