diff --git a/app/broadcast_areas/models.py b/app/broadcast_areas/models.py
index 4af79ed54..2ce313969 100644
--- a/app/broadcast_areas/models.py
+++ b/app/broadcast_areas/models.py
@@ -171,7 +171,7 @@ class CustomBroadcastArea(BaseBroadcastArea):
     @cached_property
     def count_of_phones(self):
         return sum(
-            area.polygons.ratio_of_intersection_with(self.polygons) * area.count_of_phones
+            area.simple_polygons.ratio_of_intersection_with(self.polygons) * area.count_of_phones
             for area in self.overlapping_areas
         )
 
diff --git a/tests/app/broadcast_areas/test_broadcast_area.py b/tests/app/broadcast_areas/test_broadcast_area.py
index 448b76f00..e637318e0 100644
--- a/tests/app/broadcast_areas/test_broadcast_area.py
+++ b/tests/app/broadcast_areas/test_broadcast_area.py
@@ -377,7 +377,7 @@ def test_estimated_bleed(
             'Stoke Bishop',
             'Windmill Hill',
         ],
-        73_496,
+        73_119,
     ),
     (
         SKYE,
@@ -387,7 +387,7 @@ def test_estimated_bleed(
             'Na Hearadh agus Ceann a Deas nan Loch',
             'Wester Ross, Strathpeffer and Lochalsh',
         ],
-        3_517,
+        3_534,
     ),
 ))
 def test_count_of_phones_for_custom_area(