diff --git a/src/c3nav/editor/operations.py b/src/c3nav/editor/operations.py
index a3993e7c..5ee856b5 100644
--- a/src/c3nav/editor/operations.py
+++ b/src/c3nav/editor/operations.py
@@ -247,6 +247,9 @@ class DatabaseOperationCollection(BaseSchema):
     def append(self, item: DatabaseOperation):
         self.operations.append(item)
 
+    def __getitem__(self, item):
+        return self.operations[item]
+
     def prefetch(self) -> "PrefetchedDatabaseOperationCollection":
         return PrefetchedDatabaseOperationCollection(operations=self, instances=self.prev.get_instances())
 
diff --git a/src/c3nav/editor/overlay.py b/src/c3nav/editor/overlay.py
index 743e9897..4e17aeb7 100644
--- a/src/c3nav/editor/overlay.py
+++ b/src/c3nav/editor/overlay.py
@@ -148,7 +148,8 @@ class DatabaseOverlayManager:
 
         if self.operations:
             last_change = self.operations[-1]
-            if isinstance(last_change, UpdateManyToManyOperation) and last_change == ref and last_change == field.name:
+            if (isinstance(last_change, UpdateManyToManyOperation)
+                    and last_change.obj == ref and last_change == field.name):
                 if action == "post_add":
                     last_change.add_values.update(pk_set)
                     last_change.remove_values.difference_update(pk_set)