diff --git a/changelog.d/6915.misc b/changelog.d/6915.misc
new file mode 100644
index 0000000000..3a181ef243
--- /dev/null
+++ b/changelog.d/6915.misc
@@ -0,0 +1 @@
+Add type hints to the spam checker module.
diff --git a/synapse/events/spamcheck.py b/synapse/events/spamcheck.py
index 819c03e48b..6e6d75bdcb 100644
--- a/synapse/events/spamcheck.py
+++ b/synapse/events/spamcheck.py
@@ -15,13 +15,17 @@
 # limitations under the License.
 
 import inspect
-from typing import Dict
+from typing import Dict, Optional, List
 
 from synapse.spam_checker_api import SpamCheckerApi
 
+MYPY = False
+if MYPY:
+    import synapse.server
+
 
 class SpamChecker(object):
-    def __init__(self, hs):
+    def __init__(self, hs: "synapse.server.HomeServer"):
         self.spam_checker = None
 
         module = None
@@ -41,7 +45,7 @@ class SpamChecker(object):
             else:
                 self.spam_checker = module(config=config)
 
-    def check_event_for_spam(self, event):
+    def check_event_for_spam(self, event: "synapse.events.EventBase") -> bool:
         """Checks if a given event is considered "spammy" by this server.
 
         If the server considers an event spammy, then it will be rejected if
@@ -49,10 +53,10 @@ class SpamChecker(object):
         users receive a blank event.
 
         Args:
-            event (synapse.events.EventBase): the event to be checked
+            event: the event to be checked
 
         Returns:
-            bool: True if the event is spammy.
+            True if the event is spammy.
         """
         if self.spam_checker is None:
             return False
@@ -61,34 +65,34 @@ class SpamChecker(object):
 
     def user_may_invite(
         self,
-        inviter_userid,
-        invitee_userid,
-        third_party_invite,
-        room_id,
-        new_room,
-        published_room,
-    ):
+        inviter_userid: str,
+        invitee_userid: str,
+        third_party_invite: Optional[Dict],
+        room_id: str,
+        new_room: bool,
+        published_room: bool,
+    ) -> bool:
         """Checks if a given user may send an invite
 
         If this method returns false, the invite will be rejected.
 
         Args:
-            inviter_userid (str)
-            invitee_userid (str|None): The user ID of the invitee. Is None
+            inviter_userid:
+            invitee_userid: The user ID of the invitee. Is None
                 if this is a third party invite and the 3PID is not bound to a
                 user ID.
-            third_party_invite (dict|None): If a third party invite then is a
+            third_party_invite: If a third party invite then is a
                 dict containing the medium and address of the invitee.
-            room_id (str)
-            new_room (bool): Whether the user is being invited to the room as
+            room_id:
+            new_room: Whether the user is being invited to the room as
                 part of a room creation, if so the invitee would have been
                 included in the call to `user_may_create_room`.
-            published_room (bool): Whether the room the user is being invited
+            published_room: Whether the room the user is being invited
                 to has been published in the local homeserver's public room
                 directory.
 
         Returns:
-            bool: True if the user may send an invite, otherwise False
+            True if the user may send an invite, otherwise False
         """
         if self.spam_checker is None:
             return True
@@ -103,23 +107,27 @@ class SpamChecker(object):
         )
 
     def user_may_create_room(
-        self, userid, invite_list, third_party_invite_list, cloning
-    ):
+        self,
+        userid: str,
+        invite_list: List[str],
+        third_party_invite_list: List[Dict],
+        cloning: bool,
+    ) -> bool:
         """Checks if a given user may create a room
 
         If this method returns false, the creation request will be rejected.
 
         Args:
-            userid (string): The sender's user ID
-            invite_list (list[str]): List of user IDs that would be invited to
+            userid: The ID of the user attempting to create a room
+            invite_list: List of user IDs that would be invited to
                 the new room.
-            third_party_invite_list (list[dict]): List of third party invites
+            third_party_invite_list: List of third party invites
                 for the new room.
-            cloning (bool): Whether the user is cloning an existing room, e.g.
+            cloning: Whether the user is cloning an existing room, e.g.
                 upgrading a room.
 
         Returns:
-            bool: True if the user may create a room, otherwise False
+            True if the user may create a room, otherwise False
         """
         if self.spam_checker is None:
             return True
@@ -128,34 +136,34 @@ class SpamChecker(object):
             userid, invite_list, third_party_invite_list, cloning
         )
 
-    def user_may_create_room_alias(self, userid, room_alias):
+    def user_may_create_room_alias(self, userid: str, room_alias: str) -> bool:
         """Checks if a given user may create a room alias
 
         If this method returns false, the association request will be rejected.
 
         Args:
-            userid (string): The sender's user ID
-            room_alias (string): The alias to be created
+            userid: The ID of the user attempting to create a room alias
+            room_alias: The alias to be created
 
         Returns:
-            bool: True if the user may create a room alias, otherwise False
+            True if the user may create a room alias, otherwise False
         """
         if self.spam_checker is None:
             return True
 
         return self.spam_checker.user_may_create_room_alias(userid, room_alias)
 
-    def user_may_publish_room(self, userid, room_id):
+    def user_may_publish_room(self, userid: str, room_id: str) -> bool:
         """Checks if a given user may publish a room to the directory
 
         If this method returns false, the publish request will be rejected.
 
         Args:
-            userid (string): The sender's user ID
-            room_id (string): The ID of the room that would be published
+            userid: The user ID attempting to publish the room
+            room_id: The ID of the room that would be published
 
         Returns:
-            bool: True if the user may publish the room, otherwise False
+            True if the user may publish the room, otherwise False
         """
         if self.spam_checker is None:
             return True
diff --git a/synapse/spam_checker_api/__init__.py b/synapse/spam_checker_api/__init__.py
index efcc10f808..9b78924d96 100644
--- a/synapse/spam_checker_api/__init__.py
+++ b/synapse/spam_checker_api/__init__.py
@@ -18,6 +18,10 @@ from twisted.internet import defer
 
 from synapse.storage.state import StateFilter
 
+MYPY = False
+if MYPY:
+    import synapse.server
+
 logger = logging.getLogger(__name__)
 
 
@@ -26,18 +30,18 @@ class SpamCheckerApi(object):
     access to rooms and other relevant information.
     """
 
-    def __init__(self, hs):
+    def __init__(self, hs: "synapse.server.HomeServer"):
         self.hs = hs
 
         self._store = hs.get_datastore()
 
     @defer.inlineCallbacks
-    def get_state_events_in_room(self, room_id, types):
+    def get_state_events_in_room(self, room_id: str, types: tuple) -> defer.Deferred:
         """Gets state events for the given room.
 
         Args:
-            room_id (string): The room ID to get state events in.
-            types (tuple): The event type and state key (using None
+            room_id: The room ID to get state events in.
+            types: The event type and state key (using None
                 to represent 'any') of the room state to acquire.
 
         Returns:
diff --git a/tox.ini b/tox.ini
index 0fa78a0ff7..2e12612a06 100644
--- a/tox.ini
+++ b/tox.ini
@@ -179,6 +179,7 @@ extras = all
 commands = mypy \
             synapse/api \
             synapse/config/ \
+            synapse/events/spamcheck.py \
             synapse/federation/sender \
             synapse/federation/transport \
             synapse/handlers/sync.py \