diff --git a/typings/index.d.ts b/typings/index.d.ts
index d02a4696..e29bd9c1 100644
--- a/typings/index.d.ts
+++ b/typings/index.d.ts
@@ -186,7 +186,7 @@ declare module 'react-digraph' {
     static revert(graphInput: IGraphInput): any;
   }
 
-  export type LayoutEngineType = 'None' | 'SnapToGrid' | 'VerticalTree';
+  export type LayoutEngineType = 'None' | 'SnapToGrid' | 'VerticalTree' | 'HorizontalTree';
 
   export const GraphView: React.ComponentClass<IGraphViewProps>;
   export type INodeMapNode = {