diff --git a/google.visualization/google.visualization.d.ts b/google.visualization/google.visualization.d.ts
index 11a1f780cf..f45f3f6a3b 100644
--- a/google.visualization/google.visualization.d.ts
+++ b/google.visualization/google.visualization.d.ts
@@ -244,10 +244,10 @@ declare module google {
         }
 
         export interface ChartArea {
-            top: any;
-            left: any;
-            width: any;
-            height: any;
+            top?: any;
+            left?: any;
+            width?: any;
+            height?: any;
         }
 
         export interface ChartLegend {