diff --git a/gruntjs/gruntjs.d.ts b/gruntjs/gruntjs.d.ts
index e503cb572..a3a3a67e5 100644
--- a/gruntjs/gruntjs.d.ts
+++ b/gruntjs/gruntjs.d.ts
@@ -1172,7 +1172,7 @@ declare module grunt {
             /**
              * The command to execute. It should be in the system path.
              */
-            cmd: string
+            cmd?: string
 
             /**
              * If specified, the same grunt bin that is currently running will be