diff --git a/changelog.d/10253.misc b/changelog.d/10253.misc
new file mode 100644
index 0000000000..44d9217245
--- /dev/null
+++ b/changelog.d/10253.misc
@@ -0,0 +1 @@
+Fix type hints for computing auth events.
diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index 29cf257633..f8b068e563 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
-from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple, Union
 
 import pymacaroons
 from netaddr import IPAddress
@@ -31,6 +31,7 @@ from synapse.api.errors import (
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.appservice import ApplicationService
 from synapse.events import EventBase
+from synapse.events.builder import EventBuilder
 from synapse.http import get_request_user_agent
 from synapse.http.site import SynapseRequest
 from synapse.logging import opentracing as opentracing
@@ -490,7 +491,7 @@ class Auth:
 
     def compute_auth_events(
         self,
-        event,
+        event: Union[EventBase, EventBuilder],
         current_state_ids: StateMap[str],
         for_verification: bool = False,
     ) -> List[str]:
diff --git a/synapse/event_auth.py b/synapse/event_auth.py
index 33d7c60241..89bcf81515 100644
--- a/synapse/event_auth.py
+++ b/synapse/event_auth.py
@@ -14,7 +14,7 @@
 # limitations under the License.
 
 import logging
-from typing import Any, Dict, List, Optional, Set, Tuple
+from typing import Any, Dict, List, Optional, Set, Tuple, Union
 
 from canonicaljson import encode_canonical_json
 from signedjson.key import decode_verify_key_bytes
@@ -29,6 +29,7 @@ from synapse.api.room_versions import (
     RoomVersion,
 )
 from synapse.events import EventBase
+from synapse.events.builder import EventBuilder
 from synapse.types import StateMap, UserID, get_domain_from_id
 
 logger = logging.getLogger(__name__)
@@ -724,7 +725,7 @@ def get_public_keys(invite_event: EventBase) -> List[Dict[str, Any]]:
     return public_keys
 
 
-def auth_types_for_event(event: EventBase) -> Set[Tuple[str, str]]:
+def auth_types_for_event(event: Union[EventBase, EventBuilder]) -> Set[Tuple[str, str]]:
     """Given an event, return a list of (EventType, StateKey) that may be
     needed to auth the event. The returned list may be a superset of what
     would actually be required depending on the full state of the room.
diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index 0cb9c1cc1e..6286ad999a 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -118,7 +118,7 @@ class _EventInternalMetadata:
     proactively_send = DictProperty("proactively_send")  # type: bool
     redacted = DictProperty("redacted")  # type: bool
     txn_id = DictProperty("txn_id")  # type: str
-    token_id = DictProperty("token_id")  # type: str
+    token_id = DictProperty("token_id")  # type: int
     historical = DictProperty("historical")  # type: bool
 
     # XXX: These are set by StreamWorkerStore._set_before_and_after.
diff --git a/synapse/events/builder.py b/synapse/events/builder.py
index 81bf8615b7..fb48ec8541 100644
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -12,12 +12,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
-from typing import Any, Dict, List, Optional, Tuple, Union
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple, Union
 
 import attr
 from nacl.signing import SigningKey
 
-from synapse.api.auth import Auth
 from synapse.api.constants import MAX_DEPTH
 from synapse.api.errors import UnsupportedRoomVersionError
 from synapse.api.room_versions import (
@@ -34,10 +33,14 @@ from synapse.types import EventID, JsonDict
 from synapse.util import Clock
 from synapse.util.stringutils import random_string
 
+if TYPE_CHECKING:
+    from synapse.api.auth import Auth
+    from synapse.server import HomeServer
+
 logger = logging.getLogger(__name__)
 
 
-@attr.s(slots=True, cmp=False, frozen=True)
+@attr.s(slots=True, cmp=False, frozen=True, auto_attribs=True)
 class EventBuilder:
     """A format independent event builder used to build up the event content
     before signing the event.
@@ -62,31 +65,30 @@ class EventBuilder:
         _signing_key: The signing key to use to sign the event as the server
     """
 
-    _state = attr.ib(type=StateHandler)
-    _auth = attr.ib(type=Auth)
-    _store = attr.ib(type=DataStore)
-    _clock = attr.ib(type=Clock)
-    _hostname = attr.ib(type=str)
-    _signing_key = attr.ib(type=SigningKey)
+    _state: StateHandler
+    _auth: "Auth"
+    _store: DataStore
+    _clock: Clock
+    _hostname: str
+    _signing_key: SigningKey
 
-    room_version = attr.ib(type=RoomVersion)
+    room_version: RoomVersion
 
-    room_id = attr.ib(type=str)
-    type = attr.ib(type=str)
-    sender = attr.ib(type=str)
+    room_id: str
+    type: str
+    sender: str
 
-    content = attr.ib(default=attr.Factory(dict), type=JsonDict)
-    unsigned = attr.ib(default=attr.Factory(dict), type=JsonDict)
+    content: JsonDict = attr.Factory(dict)
+    unsigned: JsonDict = attr.Factory(dict)
 
     # These only exist on a subset of events, so they raise AttributeError if
     # someone tries to get them when they don't exist.
-    _state_key = attr.ib(default=None, type=Optional[str])
-    _redacts = attr.ib(default=None, type=Optional[str])
-    _origin_server_ts = attr.ib(default=None, type=Optional[int])
+    _state_key: Optional[str] = None
+    _redacts: Optional[str] = None
+    _origin_server_ts: Optional[int] = None
 
-    internal_metadata = attr.ib(
-        default=attr.Factory(lambda: _EventInternalMetadata({})),
-        type=_EventInternalMetadata,
+    internal_metadata: _EventInternalMetadata = attr.Factory(
+        lambda: _EventInternalMetadata({})
     )
 
     @property
@@ -184,7 +186,7 @@ class EventBuilder:
 
 
 class EventBuilderFactory:
-    def __init__(self, hs):
+    def __init__(self, hs: "HomeServer"):
         self.clock = hs.get_clock()
         self.hostname = hs.hostname
         self.signing_key = hs.signing_key
@@ -193,15 +195,14 @@ class EventBuilderFactory:
         self.state = hs.get_state_handler()
         self.auth = hs.get_auth()
 
-    def new(self, room_version, key_values):
+    def new(self, room_version: str, key_values: dict) -> EventBuilder:
         """Generate an event builder appropriate for the given room version
 
         Deprecated: use for_room_version with a RoomVersion object instead
 
         Args:
-            room_version (str): Version of the room that we're creating an event builder
-                for
-            key_values (dict): Fields used as the basis of the new event
+            room_version: Version of the room that we're creating an event builder for
+            key_values: Fields used as the basis of the new event
 
         Returns:
             EventBuilder
@@ -212,13 +213,15 @@ class EventBuilderFactory:
             raise UnsupportedRoomVersionError()
         return self.for_room_version(v, key_values)
 
-    def for_room_version(self, room_version, key_values):
+    def for_room_version(
+        self, room_version: RoomVersion, key_values: dict
+    ) -> EventBuilder:
         """Generate an event builder appropriate for the given room version
 
         Args:
-            room_version (synapse.api.room_versions.RoomVersion):
+            room_version:
                 Version of the room that we're creating an event builder for
-            key_values (dict): Fields used as the basis of the new event
+            key_values: Fields used as the basis of the new event
 
         Returns:
             EventBuilder
@@ -286,15 +289,15 @@ def create_local_event_from_event_dict(
 _event_id_counter = 0
 
 
-def _create_event_id(clock, hostname):
+def _create_event_id(clock: Clock, hostname: str) -> str:
     """Create a new event ID
 
     Args:
-        clock (Clock)
-        hostname (str): The server name for the event ID
+        clock
+        hostname: The server name for the event ID
 
     Returns:
-        str
+        The new event ID
     """
 
     global _event_id_counter
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index db12abd59d..364c5cd2d3 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -509,6 +509,8 @@ class EventCreationHandler:
                 Should normally be left as None, which will cause them to be calculated
                 based on the room state at the prev_events.
 
+                If non-None, prev_event_ids must also be provided.
+
             require_consent: Whether to check if the requester has
                 consented to the privacy policy.
 
@@ -581,6 +583,9 @@ class EventCreationHandler:
         # Strip down the auth_event_ids to only what we need to auth the event.
         # For example, we don't need extra m.room.member that don't match event.sender
         if auth_event_ids is not None:
+            # If auth events are provided, prev events must be also.
+            assert prev_event_ids is not None
+
             temp_event = await builder.build(
                 prev_event_ids=prev_event_ids,
                 auth_event_ids=auth_event_ids,
@@ -784,6 +789,8 @@ class EventCreationHandler:
                 The event ids to use as the auth_events for the new event.
                 Should normally be left as None, which will cause them to be calculated
                 based on the room state at the prev_events.
+
+                If non-None, prev_event_ids must also be provided.
             ratelimit: Whether to rate limit this send.
             txn_id: The transaction ID.
             ignore_shadow_ban: True if shadow-banned users should be allowed to