diff -r 1562bdf948da -r 1b4fa55f7caa src/kv_list.c
--- a/src/kv_list.c	Wed Sep 17 22:45:00 2025 +0200
+++ b/src/kv_list.c	Thu Sep 18 00:36:42 2025 +0200
@@ -489,5 +489,26 @@
 }
 
 int cx_kv_list_insert(CxList *list, size_t index, CxHashKey key, void *value) {
-    return -1;
+    cx_kv_list *kv_list = (cx_kv_list*)list;
+
+    // add the new node via emplacement (we don't want to look up the node again)
+    void *node_data = cxListEmplaceAt(list, index);
+    if (node_data == NULL) return -1; // LCOV_EXCL_LINE
+
+    // copy the data
+    if (list->collection.store_pointer) {
+        memcpy(node_data, &value, sizeof(void*));
+    } else {
+        memcpy(node_data, value, kv_list->list.base.collection.elem_size);
+    }
+
+    // add the key to the map
+    kv_list->map_methods->put(&kv_list->map->map_base.base, key, node_data);
+    // TODO: get rid of the node again, when adding the entry to the map failed
+
+    // write the key to the node
+    CxHashKey *loc_key = cx_kv_list_loc_key(kv_list, node_data);
+    *loc_key = key;
+
+    return 0;
 }