diff --git a/core/modules/system/system.base.css b/core/modules/system/system.base.css
index b6d1ad0..7c64049 100644
--- a/core/modules/system/system.base.css
+++ b/core/modules/system/system.base.css
@@ -32,6 +32,7 @@
   background-image: url(../../misc/throbber.gif);
   background-position: 100% 2px; /* LTR */
   background-repeat: no-repeat;
+  max-width: 100%;
 }
 .js input.throbbing {
   background-position: 100% -18px; /* LTR */