diff --git a/src/array/groupBy.ts b/src/array/groupBy.ts
index 797e4a1ae..09979741a 100644
--- a/src/array/groupBy.ts
+++ b/src/array/groupBy.ts
@@ -37,7 +37,7 @@ export function groupBy<T, K extends PropertyKey>(arr: readonly T[], getKeyFromI
     const item = arr[i];
     const key = getKeyFromItem(item);
 
-    if (result[key] == null) {
+    if (!Object.hasOwn(result, key) || result[key] == null) {
       result[key] = [];
     }