diff --git a/MultiServer.py b/MultiServer.py
index 88a4a4f0..726a21f1 100644
--- a/MultiServer.py
+++ b/MultiServer.py
@@ -654,27 +654,27 @@ def get_remaining(ctx: Context, team: int, slot: int) -> typing.List[int]:
 
 def register_location_checks(ctx: Context, team: int, slot: int, locations: typing.Iterable[int]):
     new_locations = set(locations) - ctx.location_checks[team, slot]
+    new_locations.intersection_update(ctx.locations[slot])  # ignore location IDs unknown to this multidata
     if new_locations:
         ctx.client_activity_timers[team, slot] = datetime.datetime.now(datetime.timezone.utc)
         for location in new_locations:
-            if location in ctx.locations[slot]:
-                item_id, target_player = ctx.locations[slot][location]
-                new_item = NetworkItem(item_id, location, slot)
-                if target_player != slot or slot in ctx.remote_items:
-                    get_received_items(ctx, team, target_player).append(new_item)
+            item_id, target_player = ctx.locations[slot][location]
+            new_item = NetworkItem(item_id, location, slot)
+            if target_player != slot or slot in ctx.remote_items:
+                get_received_items(ctx, team, target_player).append(new_item)
 
-                logging.info('(Team #%d) %s sent %s to %s (%s)' % (
-                    team + 1, ctx.player_names[(team, slot)], get_item_name_from_id(item_id),
-                    ctx.player_names[(team, target_player)], get_location_name_from_id(location)))
-                info_text = json_format_send_event(new_item, target_player)
-                ctx.broadcast_team(team, [info_text])
+            logging.info('(Team #%d) %s sent %s to %s (%s)' % (
+                team + 1, ctx.player_names[(team, slot)], get_item_name_from_id(item_id),
+                ctx.player_names[(team, target_player)], get_location_name_from_id(location)))
+            info_text = json_format_send_event(new_item, target_player)
+            ctx.broadcast_team(team, [info_text])
 
         ctx.location_checks[team, slot] |= new_locations
         send_new_items(ctx)
         ctx.broadcast(ctx.clients[team][slot], [{
             "cmd": "RoomUpdate",
             "hint_points": get_slot_points(ctx, team, slot),
-            "checked_locations": locations,  # duplicated data, but used for coop
+            "checked_locations": new_locations,  # send back new checks only
         }])
 
         ctx.save()
diff --git a/docs/network protocol.md b/docs/network protocol.md
index 42669af4..4673b5b7 100644
--- a/docs/network protocol.md	
+++ b/docs/network protocol.md	
@@ -140,7 +140,7 @@ The arguments for RoomUpdate are identical to [RoomInfo](#RoomInfo) barring:
 | ---- | ---- | ----- |
 | hint_points | int | New argument. The client's current hint points. |
 | players | list\[NetworkPlayer\] | Changed argument. Always sends all players, whether connected or not. |
-| checked_locations | May be a partial update, containing new locations that were checked. |
+| checked_locations | May be a partial update, containing new locations that were checked, especially from a coop partner in the same slot. |
 | missing_locations | Should never be sent as an update, if needed is the inverse of checked_locations. |
 
 All arguments for this packet are optional, only changes are sent.