Index: src/wp-admin/includes/template.php
===================================================================
--- src/wp-admin/includes/template.php	(revision 47585)
+++ src/wp-admin/includes/template.php	(working copy)
@@ -922,17 +922,23 @@
  *
  * @since 2.1.0
  *
- * @param string $selected Slug for the role that should be already selected.
+ * @param string|array $selected Slug for the role that should be already selected.
  */
 function wp_dropdown_roles( $selected = '' ) {
 	$r = '';
 
+	if( ! is_array( $selected ) ){
+		$parsed_selected = explode( ",", $selected );
+	} else {
+		$parsed_selected = wp_parse_args( $selected );
+	}
+
 	$editable_roles = array_reverse( get_editable_roles() );
 
 	foreach ( $editable_roles as $role => $details ) {
 		$name = translate_user_role( $details['name'] );
 		// Preselect specified role.
-		if ( $selected == $role ) {
+		if ( in_array( $role, $parsed_selected ) ) {
 			$r .= "\n\t<option selected='selected' value='" . esc_attr( $role ) . "'>$name</option>";
 		} else {
 			$r .= "\n\t<option value='" . esc_attr( $role ) . "'>$name</option>";