diff --git a/mod/forum/templates/inpage_reply.mustache b/mod/forum/templates/inpage_reply.mustache
index 5ceb5c93c1e..de8970c382a 100644
--- a/mod/forum/templates/inpage_reply.mustache
+++ b/mod/forum/templates/inpage_reply.mustache
@@ -38,7 +38,7 @@
         <form data-post-id="{{postid}}" id="inpage-reply-{{postid}}" data-content="inpage-reply-form" action="{{{reply_url}}}">
             <div class="row pb-1">
                 <span>
-                    <textarea rows="5" name="post" title="post" class="w-100" placeholder="{{#str}} replyplaceholder, forum {{/str}}"></textarea>
+                    <textarea rows="5" name="post" title="post" class="form-control" placeholder="{{#str}} replyplaceholder, forum {{/str}}"></textarea>
                     <input type="hidden" name="postformat" value="{{postformat}}"/>
                 </span>
                 <input type="hidden" name="subject" value="{{parentsubject}}"/>