diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py
index 36c6627b4c1b..1f4902bc214b 100644
--- a/synapse/util/caches/descriptors.py
+++ b/synapse/util/caches/descriptors.py
@@ -21,6 +21,7 @@
     Awaitable,
     Callable,
     Collection,
+    Coroutine,
     Dict,
     Generic,
     Hashable,
@@ -58,7 +59,7 @@
 
 
 class CachedFunction(Generic[F]):
-    invalidate: Callable[[Tuple[Any, ...]], None]
+    invalidate: Callable[[Tuple[Any, ...]], Union[None, Coroutine]]
     invalidate_all: Callable[[], None]
     invalidate_external: Any = None
     prefill: Callable[[Tuple[Any, ...], Any], None]
diff --git a/synapse/util/caches/redis_caches.py b/synapse/util/caches/redis_caches.py
index fa77fd1776fd..d6ae353aa786 100644
--- a/synapse/util/caches/redis_caches.py
+++ b/synapse/util/caches/redis_caches.py
@@ -8,6 +8,7 @@
     Generic,
     List,
     Optional,
+    Tuple,
     Union,
     cast,
 )
@@ -75,7 +76,7 @@ async def _wrapped(self: Any, *args: Any, **kwargs: Any) -> Any:
                 await redis_shard_cache.set(cache_name, cache_key, value)
             return value
 
-        async def _invalidate(key: KT) -> None:
+        async def _invalidate(key: Tuple[Any, ...]) -> None:
             return await redis_shard_cache.delete(
                 cache_name,
                 _redis_key(key),
diff --git a/tests/handlers/test_register.py b/tests/handlers/test_register.py
index c30356ebbc34..234f8bf537ce 100644
--- a/tests/handlers/test_register.py
+++ b/tests/handlers/test_register.py
@@ -138,7 +138,7 @@ class RegistrationTestCase(unittest.HomeserverTestCase):
     """Tests the RegistrationHandler."""
 
     def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
-        reactor.advance(1)
+        reactor.advance(1)  # type: ignore
         hs_config = self.default_config()
 
         # some of the tests rely on us having a user consent version