diff --git a/core/modules/system/css/system.theme.css b/core/modules/system/css/system.theme.css
index 01ee3d182879d9e9b8efa54bb10cf2e70ac81dae..3f31462c3b4d2ba341852595143bb61417f959cb 100644
--- a/core/modules/system/css/system.theme.css
+++ b/core/modules/system/css/system.theme.css
@@ -109,7 +109,7 @@ abbr.form-required, abbr.tabledrag-changed, abbr.ajax-changed {
   content: ':';
 }
 .form-type-radios .container-inline label:after {
-  content: none;
+  content: '';
 }
 .form-type-radios .container-inline .form-type-radio {
   margin: 0 1em;