diff --git a/server/api/models/comment.js b/server/api/models/comment.js
index 7b836812..793ab8e0 100644
--- a/server/api/models/comment.js
+++ b/server/api/models/comment.js
@@ -2,7 +2,7 @@
 module.exports = (sequelize, DataTypes) => {
   const comment = sequelize.define('comment', {
     activitypub_id: {
-      type: DataTypes.STRING(18),
+      type: DataTypes.STRING,
       index: true,
       unique: true
     },
diff --git a/server/migrations/20191112101545-ap_comment_id.js b/server/migrations/20191112101545-ap_comment_id.js
new file mode 100644
index 00000000..6a7f2b4d
--- /dev/null
+++ b/server/migrations/20191112101545-ap_comment_id.js
@@ -0,0 +1,19 @@
+'use strict';
+
+module.exports = {
+  up: (queryInterface, Sequelize) => {
+    return queryInterface.changeColumn('comments', 'activitypub_id', {
+      type: Sequelize.STRING,
+      index: true,
+      unique: true
+    })
+  },
+
+  down: (queryInterface, Sequelize) => {
+    return queryInterface.changeColumn('comments', 'activitypub_id', {
+      type: Sequelize.STRING(18),
+      index: true,
+      unique: true
+    })
+  }
+}