diff --git a/framework/core/src/Post/Post.php b/framework/core/src/Post/Post.php
index 8c508aa9a..8c72f6c53 100644
--- a/framework/core/src/Post/Post.php
+++ b/framework/core/src/Post/Post.php
@@ -98,7 +98,7 @@ class Post extends AbstractModel
             $db = static::getConnectionResolver();
             $post->number = new Expression('('.$db
                     ->table('posts', 'pn')
-                    ->whereRaw('pn.discussion_id = '.intval($post->discussion_id))
+                    ->whereRaw($db->getTablePrefix().'pn.discussion_id = '.intval($post->discussion_id))
                     ->select($db->raw('max('.$db->getTablePrefix().'pn.number) + 1'))
                     ->toSql()
                 .')');