diff --git a/ace/ace.d.ts b/ace/ace.d.ts
index 29fadf3bc7..9866e1e28b 100644
--- a/ace/ace.d.ts
+++ b/ace/ace.d.ts
@@ -576,7 +576,7 @@ declare module AceAjax {
         /**
          * Returns the current tab size.
         **/
-        getTabSize(): string;
+        getTabSize(): number;
 
         /**
          * Returns `true` if the character at the position is a soft tab.