diff --git a/packages/react-json-tree/src/types.ts b/packages/react-json-tree/src/types.ts
index 70cde159..79cc7d88 100644
--- a/packages/react-json-tree/src/types.ts
+++ b/packages/react-json-tree/src/types.ts
@@ -40,7 +40,7 @@ interface JSONNestedNodeCircularPropsPassedThroughJSONTree {
   postprocessValue: (value: any) => any;
   isCustomNode: (value: any) => boolean;
   collectionLimit: number;
-  sortObjectKeys?: (a: any, b: any) => number | boolean;
+  sortObjectKeys?: ((a: any, b: any) => number) | boolean;
 }
 export type CircularPropsPassedThroughJSONTree = SharedCircularPropsPassedThroughJSONTree &
   JSONValueNodeCircularPropsPassedThroughJSONTree &