diff --git a/src/react-sortable-tree.js b/src/react-sortable-tree.js
index 1c4fb743..54b2716f 100644
--- a/src/react-sortable-tree.js
+++ b/src/react-sortable-tree.js
@@ -770,7 +770,9 @@ class ReactSortableTree extends Component {
 }
 
 ReactSortableTree.propTypes = {
-  dragDropManager: PropTypes.shape({}).isRequired,
+  dragDropManager: PropTypes.shape({
+    getMonitor: PropTypes.func,
+  }).isRequired,
 
   // Tree data in the following format:
   // [{title: 'main', subtitle: 'sub'}, { title: 'value2', expanded: true, children: [{ title: 'value3') }] }]