diff --git a/ace/ace.d.ts b/ace/ace.d.ts
index 8fed295f2..ae4a83f8e 100644
--- a/ace/ace.d.ts
+++ b/ace/ace.d.ts
@@ -2244,7 +2244,7 @@ declare module AceAjax {
          * @param range The range of text to select
          * @param reverse Indicates if the range should go backwards (`true`) or not
         **/
-        setRange(range: Range, reverse: boolean): void;
+        setRange(range: Range, reverse?: boolean): void;
 
         /**
          * Moves the selection cursor to the indicated row and column.