diff --git a/vacuum_gambit.p8 b/vacuum_gambit.p8
index 611e96f..8b73701 100644
--- a/vacuum_gambit.p8
+++ b/vacuum_gambit.p8
@@ -258,8 +258,12 @@ function updategame()
 	-- many bullets and many enemy ships;
 	-- use bucket collider for efficiency
 
- local eship_collider = collider.new()
- eships:strip(function(s) eship_collider:insert(s) end)
+ local eship_collider, pp = collider.new(), eships
+ eships:strip(function(s)
+  eship_collider:insert(s)
+  s.prev = pp
+  pp = s
+end)
 
  -- lose tokens, save time:
  -- unroll `strip` to avoid