diff --git a/packages/material-ui/src/Slide/Slide.d.ts b/packages/material-ui/src/Slide/Slide.d.ts
index b35d061ac36bf3..4bdfeb8da95201 100644
--- a/packages/material-ui/src/Slide/Slide.d.ts
+++ b/packages/material-ui/src/Slide/Slide.d.ts
@@ -4,7 +4,7 @@ import { TransitionProps } from '../transitions/transition';
 
 export interface SlideProps extends TransitionProps {
   children?: React.ReactElement<any, any>;
-  direction: 'left' | 'right' | 'up' | 'down';
+  direction?: 'left' | 'right' | 'up' | 'down';
   ref?: React.Ref<unknown>;
   theme?: Theme;
 }