diff --git a/activity.py b/activity.py
index 986943d..4b974d5 100644
--- a/activity.py
+++ b/activity.py
@@ -247,7 +247,14 @@ def _on_entry_activate(self, entry):
     def _on_entry_changed(self, entry):
         """Update internal state as user types."""
         if not self.game.game_completed:
-            self.game.current_equation = entry.get_text()
+            text = entry.get_text()
+            for broken in self.game.broken_buttons:
+                if str(broken) in text:
+                    text = text.replace(str(broken), "")
+                    entry.set_text(text)
+                    entry.set_position(-1)
+                    return
+            self.game.current_equation = text
 
     def _on_button_clicked(self, button):
         value = button.game_value