diff --git a/lib/filterx/func-flatten.c b/lib/filterx/func-flatten.c
index bcda2ec8f..444bd3d49 100644
--- a/lib/filterx/func-flatten.c
+++ b/lib/filterx/func-flatten.c
@@ -76,7 +76,7 @@ _collect_modifications_from_elem(FilterXObject *key, FilterXObject *value, gpoin
   if (filterx_object_is_type(dict, &FILTERX_TYPE_NAME(dict)))
     {
       if (is_top_level)
-        *top_level_dict_keys = g_list_prepend(*top_level_dict_keys, filterx_object_ref(key));
+        *top_level_dict_keys = g_list_append(*top_level_dict_keys, filterx_object_ref(key));
 
       gssize orig_len = key_buffer->len;
       if (!filterx_object_repr_append(key, key_buffer))
@@ -108,7 +108,7 @@ _collect_modifications_from_elem(FilterXObject *key, FilterXObject *value, gpoin
     }
 
   FilterXObject *flat_key = filterx_string_new(key_buffer->str, (gssize) MIN(key_buffer->len, G_MAXSSIZE));
-  *flattened_kvs = g_list_prepend(*flattened_kvs, _kv_new(flat_key, value));
+  *flattened_kvs = g_list_append(*flattened_kvs, _kv_new(flat_key, value));
   filterx_object_unref(flat_key);
 
   g_string_truncate(key_buffer, orig_len);
diff --git a/lib/filterx/tests/test_func_flatten.c b/lib/filterx/tests/test_func_flatten.c
index 16f30096f..996bb6615 100644
--- a/lib/filterx/tests/test_func_flatten.c
+++ b/lib/filterx/tests/test_func_flatten.c
@@ -111,7 +111,7 @@ Test(filterx_func_flatten, default_separator)
   GList *args = g_list_append(NULL, filterx_function_arg_new(NULL,
                                                              filterx_literal_new(filterx_json_new_from_repr(input, -1))));
   _assert_flatten(args,
-                  "{\"top_level_field\":42,\"top_level_dict.inner_dict.inner_inner_field\":1,\"top_level_dict.inner_field\":1337}");
+                  "{\"top_level_field\":42,\"top_level_dict.inner_field\":1337,\"top_level_dict.inner_dict.inner_inner_field\":1}");
 }
 
 Test(filterx_func_flatten, custom_separator)
@@ -122,7 +122,7 @@ Test(filterx_func_flatten, custom_separator)
                                                              filterx_literal_new(filterx_json_new_from_repr(input, -1))));
   args = g_list_append(args, filterx_function_arg_new("separator", filterx_literal_new(filterx_string_new("->", -1))));
   _assert_flatten(args,
-                  "{\"top_level_field\":42,\"top_level_dict->inner_dict->inner_inner_field\":1,\"top_level_dict->inner_field\":1337}");
+                  "{\"top_level_field\":42,\"top_level_dict->inner_field\":1337,\"top_level_dict->inner_dict->inner_inner_field\":1}");
 }
 
 static void
diff --git a/tests/light/functional_tests/filterx/test_filterx.py b/tests/light/functional_tests/filterx/test_filterx.py
index b6e6200c5..22309a51f 100644
--- a/tests/light/functional_tests/filterx/test_filterx.py
+++ b/tests/light/functional_tests/filterx/test_filterx.py
@@ -1956,8 +1956,8 @@ def test_flatten(config, syslog_ng):
     assert file_true.get_stats()["processed"] == 1
     assert "processed" not in file_false.get_stats()
     assert file_true.read_log() == '[' \
-        '{"top_level_field":42,"top_level_dict.inner_dict.inner_inner_field":1,"top_level_dict.inner_field":1337},' \
-        '{"top_level_field":42,"top_level_dict->inner_dict->inner_inner_field":1,"top_level_dict->inner_field":1337}' \
+        '{"top_level_field":42,"top_level_dict.inner_field":1337,"top_level_dict.inner_dict.inner_inner_field":1},' \
+        '{"top_level_field":42,"top_level_dict->inner_field":1337,"top_level_dict->inner_dict->inner_inner_field":1}' \
         ']\n'