diff --git a/types/react-transition-group/CSSTransition.d.ts b/types/react-transition-group/CSSTransition.d.ts
index 16ba500270..8d48a48ce8 100644
--- a/types/react-transition-group/CSSTransition.d.ts
+++ b/types/react-transition-group/CSSTransition.d.ts
@@ -33,7 +33,7 @@ declare namespace CSSTransition {
      * ```
      */
     interface CSSTransitionProps extends TransitionProps {
-        classNames: string | CSSTransitionClassNames;
+        classNames?: string | CSSTransitionClassNames;
     }
 }
 
diff --git a/types/react-transition-group/index.d.ts b/types/react-transition-group/index.d.ts
index 2d97f64ce6..de0e099b14 100644
--- a/types/react-transition-group/index.d.ts
+++ b/types/react-transition-group/index.d.ts
@@ -1,4 +1,4 @@
-// Type definitions for react-transition-group 2.0
+// Type definitions for react-transition-group 2.8
 // Project: https://github.com/reactjs/react-transition-group
 // Definitions by: Karol Janyst <https://github.com/LKay>
 //                 Epskampie <https://github.com/Epskampie>
diff --git a/types/react-transition-group/react-transition-group-tests.tsx b/types/react-transition-group/react-transition-group-tests.tsx
index c7fb1aede0..f568642a90 100644
--- a/types/react-transition-group/react-transition-group-tests.tsx
+++ b/types/react-transition-group/react-transition-group-tests.tsx
@@ -120,6 +120,10 @@ const Test: React.StatelessComponent = () => {
             >
                 <div>{ "test" }</div>
             </CSSTransition>
+
+            <CSSTransition timeout={ 100 }>
+                <div>{ "test" }</div>
+            </CSSTransition>
         </TransitionGroup>
     );
 };