diff --git a/app/javascript/styles/mastodon/components.scss b/app/javascript/styles/mastodon/components.scss
index 7f2207c154..48386675ce 100644
--- a/app/javascript/styles/mastodon/components.scss
+++ b/app/javascript/styles/mastodon/components.scss
@@ -3109,6 +3109,10 @@ $ui-header-height: 55px;
 }
 
 .compose-form__highlightable {
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
+  flex: 0 1 auto;
   border-radius: 4px;
   transition: box-shadow 300ms linear;