diff --git a/index.js b/index.js
index 12b29e3..64e691d 100644
--- a/index.js
+++ b/index.js
@@ -81,11 +81,12 @@ function is_nil (obj) {
 /**
  * filter nested objects
  *
- * @param {Array<object>} data
+ * @param {Array<object>} input
  * @param {Array<{field: string, filter: RegExp}>} filters
  * @returns {Array<object>} filtered data
  */
-function recursive_filter (data, filters, children_key = 'children') {
+function recursive_filter (input, filters, children_key = 'children') {
+  const data = copy_object (input);
   const filtered = [];
   for (const e of data) {
     let match = true;