diff --git a/components/modal/Modal.tsx b/components/modal/Modal.tsx
index 3e3af69ac8..6182e1fe04 100644
--- a/components/modal/Modal.tsx
+++ b/components/modal/Modal.tsx
@@ -40,7 +40,7 @@ export interface ModalProps {
   transitionName?: string;
   className?: string;
   getContainer?: (instance: React.ReactInstance) => HTMLElement;
-  zIndex?: boolean;
+  zIndex?: number;
 }
 
 export interface ModalContext {