diff --git a/src/addons/mod/forum/components/post/post.ts b/src/addons/mod/forum/components/post/post.ts
index a9f5cc381..a7021eee4 100644
--- a/src/addons/mod/forum/components/post/post.ts
+++ b/src/addons/mod/forum/components/post/post.ts
@@ -259,6 +259,7 @@ export class AddonModForumPostComponent implements OnInit, OnDestroy, OnChanges
                 forum: this.forum,
             },
             backdropDismiss: false,
+            cssClass: 'core-modal-fullscreen',
         });
 
         if (!modalData) {