diff --git a/ttrs.py b/ttrs.py
index 6576326..221beb0 100755
--- a/ttrs.py
+++ b/ttrs.py
@@ -250,7 +250,9 @@ class TestTtrsPlayer(TtrsPlayer):
         self.__process_events()
         return self.__quit
 
- 
+    def reset_rotate(self):
+        pass
+
 class BalanceTtrsPlayer(TtrsPlayer):
     def __init__(self, playground, addr, player_id):
         self.playground = playground
@@ -359,12 +361,14 @@ class TtrsGame():
                         if b.pos.y in to_remove:
                             self.playground.blocks.remove(b)
 
+                    to_add = set()
                     for b in list(self.playground.blocks):
                         o = len(list(filter(lambda y: y > b.pos.y, to_remove)))
                         if o > 0:
                             self.playground.blocks.remove(b)
                             newb = Block(b.pos + Point(0, o), b.color)
-                            self.playground.blocks.add(newb)
+                            to_add.add(newb)
+                    self.playground.blocks.update(to_add)
 
             if ticks - lastfall >= FALL_INTERVAL or self.player.get_drop():
                 lastfall = ticks