diff --git a/lib/localiser/localisation/tag/filter.ex b/lib/localiser/localisation/tag/filter.ex
index f79d26d..bdd74c2 100644
--- a/lib/localiser/localisation/tag/filter.ex
+++ b/lib/localiser/localisation/tag/filter.ex
@@ -93,12 +93,23 @@ defmodule Localiser.Localisation.Tag.Filter do
     end
   end
 
-  # Room geometry changed: reload the rooms cache so containment checks stay accurate.
   @impl true
-  def handle_info({event, _}, state) when event in [:room_created, :room_updated] do
+  def handle_info({:room_created, _room}, state) do
     {:noreply, %{state | rooms: load_rooms()}}
   end
 
+  def handle_info({:room_updated, updated_room}, state) do
+    new_rooms = load_rooms()
+    old_room  = Enum.find(state.rooms, &(&1.id == updated_room.id))
+
+    if geometry_changed?(old_room, updated_room) do
+      {:ok, new_filter_state} = state.filter_module.init([], rooms: new_rooms)
+      {:noreply, %{state | rooms: new_rooms, filter_state: new_filter_state}}
+    else
+      {:noreply, %{state | rooms: new_rooms}}
+    end
+  end
+
   def handle_info({:room_deleted, _room_id, _floor_id}, state) do
     {:noreply, %{state | rooms: load_rooms()}}
   end
@@ -131,6 +142,12 @@ defmodule Localiser.Localisation.Tag.Filter do
     |> Enum.flat_map(& &1.rooms)
   end
 
+  defp geometry_changed?(nil, _), do: true
+  defp geometry_changed?(old, new) do
+    old.x != new.x or old.y != new.y or
+      old.width != new.width or old.height != new.height
+  end
+
   defp find_room(rooms, x, y) do
     Enum.find(rooms, fn room ->
       ox = room.x || 0.0