diff --git a/src/locations.cpp b/src/locations.cpp
index 9bcf7e33c260..044b9814a525 100644
--- a/src/locations.cpp
+++ b/src/locations.cpp
@@ -413,12 +413,15 @@ item_location_type vehicle_item_location::where() const
 
 detached_ptr<item> vehicle_item_location::detach( item *it )
 {
-    return veh->get_part_hack( hack_id ).remove_item( *it );
+    detached_ptr<item> ret = veh->get_part_hack( hack_id ).remove_item( *it );
+    veh->invalidate_mass();
+    return ret;
 }
 
 void vehicle_item_location::attach( detached_ptr<item> &&obj )
 {
     veh->get_part_hack( hack_id ).add_item( std::move( obj ) );
+    veh->invalidate_mass();
 }
 
 int vehicle_item_location::obtain_cost( const Character &ch, int qty, const item *it ) const