diff --git a/ghost/core/core/server/data/migrations/versions/5.100/2024-12-01-18-54-00-add-unique-tag-post-relationship.js b/ghost/core/core/server/data/migrations/versions/5.100/2024-12-01-18-54-00-add-unique-tag-post-relationship.js
new file mode 100644
index 000000000000..e026ced0ff90
--- /dev/null
+++ b/ghost/core/core/server/data/migrations/versions/5.100/2024-12-01-18-54-00-add-unique-tag-post-relationship.js
@@ -0,0 +1,9 @@
+const {createIrreversibleMigration} = require('../../utils');
+const {addUnique} = require('../../../schema/commands');
+const logging = require('@tryghost/logging');
+
+module.exports = createIrreversibleMigration(async (knex) => {
+    logging.info('Adding unique constraint to tag-post relationship');
+
+    await addUnique('posts_tags', ['tag_id', 'post_id'], knex);
+});
diff --git a/ghost/core/package.json b/ghost/core/package.json
index f42e671c5b76..f8bc29e43e9a 100644
--- a/ghost/core/package.json
+++ b/ghost/core/package.json
@@ -1,6 +1,6 @@
 {
   "name": "ghost",
-  "version": "5.101.6",
+  "version": "5.102.0",
   "description": "The professional publishing platform",
   "author": "Ghost Foundation",
   "homepage": "https://ghost.org",
diff --git a/ghost/posts-service/lib/PostsService.js b/ghost/posts-service/lib/PostsService.js
index 98cf806dd149..147e11bbc9bd 100644
--- a/ghost/posts-service/lib/PostsService.js
+++ b/ghost/posts-service/lib/PostsService.js
@@ -362,7 +362,7 @@ class PostsService {
             }));
         }, []);
 
-        await options.transacting('posts_tags').insert(postTags);
+        await options.transacting('posts_tags').insert(postTags).onConflict().ignore();
         await this.models.Post.addActions('edited', postRows.map(p => p.id), options);
 
         return {