diff --git a/synapse/api/filtering.py b/synapse/api/filtering.py
index 34dd12368..3504585b5 100644
--- a/synapse/api/filtering.py
+++ b/synapse/api/filtering.py
@@ -142,12 +142,12 @@ USER_FILTER_SCHEMA = {
 
 @FormatChecker.cls_checks("matrix_room_id")
 def matrix_room_id_validator(room_id: object) -> bool:
-    return isinstance(room_id, str) and RoomID.is_valid(room_id)
+    return isinstance(room_id, str) and (RoomID.is_valid(room_id) or room_id == "*")
 
 
 @FormatChecker.cls_checks("matrix_user_id")
 def matrix_user_id_validator(user_id: object) -> bool:
-    return isinstance(user_id, str) and UserID.is_valid(user_id)
+    return isinstance(user_id, str) and (UserID.is_valid(user_id) or user_id == "*")
 
 
 class Filtering: