diff --git a/mathics_scanner/feed.py b/mathics_scanner/feed.py
index a4ef1f4..bedd480 100644
--- a/mathics_scanner/feed.py
+++ b/mathics_scanner/feed.py
@@ -5,7 +5,7 @@
 """
 
 from abc import ABCMeta, abstractmethod
-from typing import Callable, Optional
+from typing import Callable, List, Optional, Tuple
 
 
 class LineFeeder(metaclass=ABCMeta):
@@ -20,7 +20,7 @@ def __init__(self, filename: str):
         :param filename: A string that describes the source of the feeder, i.e.
                          the filename that is being feed.
         """
-        self.messages: list = []
+        self.messages: List[Tuple[str, str, List[str]]] = []
         self.lineno = 0
         self.filename = filename