diff --git a/django/contrib/admin/static/admin/css/forms.css b/django/contrib/admin/static/admin/css/forms.css
index 0ecfca784c..9d39b3fe89 100644
--- a/django/contrib/admin/static/admin/css/forms.css
+++ b/django/contrib/admin/static/admin/css/forms.css
@@ -268,6 +268,7 @@ body.popup .submit-row {
     margin: 0;
     background: #fff;
     border: none;
+    width: 100%;
 }
 
 .inline-related fieldset.module h3 {