diff --git a/core/modules/system/system.base.css b/core/modules/system/system.base.css
index 233c6d7..588b5b2 100644
--- a/core/modules/system/system.base.css
+++ b/core/modules/system/system.base.css
@@ -27,9 +27,7 @@
   cursor: default;
   white-space: pre;
 }
-input.form-autocomplete {
-  max-width: 100%;
-}
+
 /* Animated throbber */
 .js input.form-autocomplete {
   background-image: url(../../misc/throbber.gif);
@@ -177,6 +175,16 @@ tr .ajax-progress-throbber .throbber {
 }
 
 /**
+ *  Keep form elements from breaking the box.
+ */
+input {
+  max-width: 100%;
+  -moz-box-sizing: border-box;
+  -webkit-box-sizing: border-box;
+  box-sizing: border-box;
+}
+
+/**
  * Inline items.
  */
 .container-inline div,