diff --git a/app/models/post.rb b/app/models/post.rb
index 29645eb87..97dd5d7f9 100644
--- a/app/models/post.rb
+++ b/app/models/post.rb
@@ -589,6 +589,7 @@ class Post < ApplicationRecord
     end
 
     def merge_old_changes
+      reset_tag_array_cache
       @removed_tags = []
 
       if old_tag_string