diff --git a/src/wp-includes/css/media-views.css b/src/wp-includes/css/media-views.css
index 7d25cbd061..23ba132f54 100644
--- a/src/wp-includes/css/media-views.css
+++ b/src/wp-includes/css/media-views.css
@@ -463,6 +463,8 @@
 .compat-item .field textarea {
 	width: 100%;
 	margin: 0;
+	-webkit-box-sizing: border-box;
+	-moz-box-sizing: border-box;
 	box-sizing: border-box;
 }