diff --git a/public/assets/form/form.css b/public/assets/form/form.css
index f7b9a736d..537fe64da 100644
--- a/public/assets/form/form.css
+++ b/public/assets/form/form.css
@@ -13,6 +13,7 @@
 .zammad-form .form-control {
   display: block;
   width: 100%;
+  box-sizing: border-box;
 }
 
 .zammad-form .has-error .form-control {
@@ -69,4 +70,4 @@
     vertical-align: middle;
     box-shadow: 0 0 50px rgba(0,0,0,.3);
     color: #949494;
-}
\ No newline at end of file
+}