diff --git a/beets/autotag/__init__.py b/beets/autotag/__init__.py
index 916906029..339e3826c 100644
--- a/beets/autotag/__init__.py
+++ b/beets/autotag/__init__.py
@@ -14,7 +14,9 @@
 
 """Facilities for automatically determining files' correct metadata.
 """
+from typing import Mapping
 
+from beets.library import Item
 
 from beets import logging
 from beets import config
@@ -71,7 +73,7 @@ SPECIAL_FIELDS = {
 
 # Additional utilities for the main interface.
 
-def apply_item_metadata(item, track_info):
+def apply_item_metadata(item: Item, track_info: TrackInfo):
     """Set an item's metadata from its matched TrackInfo object.
     """
     item.artist = track_info.artist
@@ -95,7 +97,7 @@ def apply_item_metadata(item, track_info):
     # and track number). Perhaps these should be emptied?
 
 
-def apply_metadata(album_info, mapping):
+def apply_metadata(album_info: AlbumInfo, mapping: Mapping[Item, TrackInfo]):
     """Set the items' metadata to match an AlbumInfo object using a
     mapping from Items to TrackInfo objects.
     """
diff --git a/beets/autotag/hooks.py b/beets/autotag/hooks.py
index c09e4d321..a1cd49d19 100644
--- a/beets/autotag/hooks.py
+++ b/beets/autotag/hooks.py
@@ -55,7 +55,7 @@ class AttrDict(dict):
     def __setattr__(self, key, value):
         self.__setitem__(key, value)
 
-    def __hash__(self):
+    def __hash__(self) -> int:
         return id(self)