diff --git a/tests/test_docs/base.py b/tests/test_docs/base.py
index 3bf6cf9..3a142fe 100644
--- a/tests/test_docs/base.py
+++ b/tests/test_docs/base.py
@@ -23,7 +23,7 @@
 MISTUNE_BLOCK_CODE_ID = "block_code"
 
 
-def compile_and_exec(code: str, locals_dict: Dict = None) -> Dict:
+def compile_and_exec(code: str, locals_dict: Optional[Dict] = None) -> Dict:
     """
     Compile and exec the code.