diff --git a/packages/material-tree-renderer/src/resources/resource-set.ts b/packages/material-tree-renderer/src/resources/resource-set.ts
index d19a449aa..f1b72699e 100644
--- a/packages/material-tree-renderer/src/resources/resource-set.ts
+++ b/packages/material-tree-renderer/src/resources/resource-set.ts
@@ -33,7 +33,7 @@ export interface ResourceSet {
   /**
    * Remove all registered resources from the ResourceSet.
    */
-  clear();
+  clear(): void;
 }
 
 export class ResourceSetImpl implements ResourceSet {