diff --git a/modules/blogging/src/Volo.Blogging.Application/Volo/Blogging/Posts/PostAppService.cs b/modules/blogging/src/Volo.Blogging.Application/Volo/Blogging/Posts/PostAppService.cs
index 44b8e9866e..76c9a29221 100644
--- a/modules/blogging/src/Volo.Blogging.Application/Volo/Blogging/Posts/PostAppService.cs
+++ b/modules/blogging/src/Volo.Blogging.Application/Volo/Blogging/Posts/PostAppService.cs
@@ -202,7 +202,7 @@ namespace Volo.Blogging.Posts
 
         private async Task RemoveOldTags(ICollection<string> newTags, Post post)
         {
-            foreach (var oldTag in post.Tags)
+            foreach (var oldTag in post.Tags.ToList())
             {
                 var tag = await _tagRepository.GetAsync(oldTag.TagId);