diff --git a/changelog.d/14685.misc b/changelog.d/14685.misc
new file mode 100644
index 000000000..3ba227010
--- /dev/null
+++ b/changelog.d/14685.misc
@@ -0,0 +1 @@
+Improve type annotations for the helper methods on a `CachedFunction`.
\ No newline at end of file
diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py
index 72227359b..81df71a0c 100644
--- a/synapse/util/caches/descriptors.py
+++ b/synapse/util/caches/descriptors.py
@@ -53,9 +53,9 @@ F = TypeVar("F", bound=Callable[..., Any])
 
 
 class CachedFunction(Generic[F]):
-    invalidate: Any = None
-    invalidate_all: Any = None
-    prefill: Any = None
+    invalidate: Callable[[Tuple[Any, ...]], None]
+    invalidate_all: Callable[[], None]
+    prefill: Callable[[Tuple[Any, ...], Any], None]
     cache: Any = None
     num_args: Any = None