Index: src/wp-includes/category-template.php
===================================================================
--- src/wp-includes/category-template.php	(revision 49687)
+++ src/wp-includes/category-template.php	(working copy)
@@ -398,7 +398,7 @@
 	$categories = get_terms( $get_terms_args );
 
 	$name     = esc_attr( $parsed_args['name'] );
-	$class    = esc_attr( $parsed_args['class'] );
+	$class    = sanitize_html_class( $parsed_args['class'] );
 	$id       = $parsed_args['id'] ? esc_attr( $parsed_args['id'] ) : $name;
 	$required = $parsed_args['required'] ? 'required' : '';