diff --git a/app/javascript/styles/mastodon/components.scss b/app/javascript/styles/mastodon/components.scss
index d892c008bc2..2fc195a3bdc 100644
--- a/app/javascript/styles/mastodon/components.scss
+++ b/app/javascript/styles/mastodon/components.scss
@@ -10916,6 +10916,7 @@ noscript {
 }
 
 .content-warning {
+  box-sizing: border-box;
   background: rgba($ui-highlight-color, 0.05);
   color: $secondary-text-color;
   border-top: 1px solid;