diff --git a/src/wp-admin/includes/plugin.php b/src/wp-admin/includes/plugin.php
index ef6494e635..968f6e383d 100644
--- a/src/wp-admin/includes/plugin.php
+++ b/src/wp-admin/includes/plugin.php
@@ -1834,7 +1834,7 @@ function unregister_setting( $option_group, $option_name, $sanitize_callback = '
 		$option_group = 'reading';
 	}
 
-	$pos = array_search( $option_name, (array) $new_whitelist_options );
+	$pos = array_search( $option_name, (array) $new_whitelist_options[ $option_group ] );
 	if ( $pos !== false )
 		unset( $new_whitelist_options[ $option_group ][ $pos ] );
 	if ( $sanitize_callback != '' )