diff --git a/src/createGridComponent.js b/src/createGridComponent.js
index ae23adb..86ef14e 100644
--- a/src/createGridComponent.js
+++ b/src/createGridComponent.js
@@ -500,7 +500,7 @@ export default function createGridComponent({
     };
 
     _getItemStyleCache: (_: any, __: any) => ItemStyleCache;
-    _getItemStyleCache = memoizeOne((_, __) => ({}));
+    _getItemStyleCache = memoizeOne((_: any, __: any) => ({}));
 
     _getHorizontalRangeToRender(): [number, number, number, number] {
       const { columnCount, overscanCount, rowCount } = this.props;
diff --git a/src/createListComponent.js b/src/createListComponent.js
index 94e6fcd..8e54fab 100644
--- a/src/createListComponent.js
+++ b/src/createListComponent.js
@@ -410,7 +410,7 @@ export default function createListComponent({
     };
 
     _getItemStyleCache: (_: any) => ItemStyleCache;
-    _getItemStyleCache = memoizeOne(_ => ({}));
+    _getItemStyleCache = memoizeOne((_: any) => ({}));
 
     _getRangeToRender(): [number, number, number, number] {
       const { itemCount, overscanCount } = this.props;