diff --git a/extensions/mentions/js/src/forum/addComposerAutocomplete.js b/extensions/mentions/js/src/forum/addComposerAutocomplete.js
index 09808a56a..a4f02e20e 100644
--- a/extensions/mentions/js/src/forum/addComposerAutocomplete.js
+++ b/extensions/mentions/js/src/forum/addComposerAutocomplete.js
@@ -5,12 +5,9 @@ import TextEditorButton from 'flarum/common/components/TextEditorButton';
 import KeyboardNavigatable from 'flarum/common/utils/KeyboardNavigatable';
 
 import AutocompleteDropdown from './fragments/AutocompleteDropdown';
-import MentionFormats from './mentionables/formats/MentionFormats';
 import MentionableModels from './mentionables/MentionableModels';
 
 export default function addComposerAutocomplete() {
-  app.mentionFormats = new MentionFormats();
-
   const $container = $('<div class="ComposerBody-mentionsDropdownContainer"></div>');
   const dropdown = new AutocompleteDropdown();
 
diff --git a/extensions/mentions/js/src/forum/extenders/Mentionables.ts b/extensions/mentions/js/src/forum/extenders/Mentionables.ts
index cf2db51f7..46423ae54 100644
--- a/extensions/mentions/js/src/forum/extenders/Mentionables.ts
+++ b/extensions/mentions/js/src/forum/extenders/Mentionables.ts
@@ -5,7 +5,7 @@ import type MentionFormat from '../mentionables/formats/MentionFormat';
 
 export default class Mentionables implements IExtender<ForumApplication> {
   protected formats: (new () => MentionFormat)[] = [];
-  protected mentionables: Record<string, (new () => MentionableModel)[]> = {};
+  protected mentionables: Record<string, (new (...args: any[]) => MentionableModel)[]> = {};
 
   /**
    * Register a new mention format.
@@ -26,7 +26,7 @@ export default class Mentionables implements IExtender<ForumApplication> {
    * @param mentionable The mentionable instance to register.
    *                    Must extend MentionableModel.
    */
-  mentionable(symbol: string, mentionable: new () => MentionableModel): this {
+  mentionable(symbol: string, mentionable: new (...args: any[]) => MentionableModel): this {
     if (!this.mentionables[symbol]) {
       this.mentionables[symbol] = [];
     }
diff --git a/extensions/mentions/js/src/forum/index.js b/extensions/mentions/js/src/forum/index.js
index 7323a00d7..56424cedf 100644
--- a/extensions/mentions/js/src/forum/index.js
+++ b/extensions/mentions/js/src/forum/index.js
@@ -13,11 +13,14 @@ import addComposerAutocomplete from './addComposerAutocomplete';
 import PostMentionedNotification from './components/PostMentionedNotification';
 import UserMentionedNotification from './components/UserMentionedNotification';
 import GroupMentionedNotification from './components/GroupMentionedNotification';
+import MentionFormats from './mentionables/formats/MentionFormats';
 import UserPage from 'flarum/forum/components/UserPage';
 import LinkButton from 'flarum/common/components/LinkButton';
 import User from 'flarum/common/models/User';
 import Model from 'flarum/common/Model';
 
+app.mentionFormats = new MentionFormats();
+
 export { default as extend } from './extend';
 
 app.initializers.add('flarum-mentions', function () {
diff --git a/extensions/mentions/js/src/forum/mentionables/formats/HashMentionFormat.ts b/extensions/mentions/js/src/forum/mentionables/formats/HashMentionFormat.ts
index a01bf00e9..ef30d50c9 100644
--- a/extensions/mentions/js/src/forum/mentionables/formats/HashMentionFormat.ts
+++ b/extensions/mentions/js/src/forum/mentionables/formats/HashMentionFormat.ts
@@ -4,7 +4,7 @@ import TagMention from '../TagMention';
 
 export default class HashMentionFormat extends MentionFormat {
   public mentionables: (new (...args: any[]) => MentionableModel)[] = [TagMention];
-  protected extendable: boolean = false;
+  protected extendable: boolean = true;
 
   public trigger(): string {
     return '#';