diff --git a/src/Helpers/Arr.php b/src/Helpers/Arr.php
index bd83f3f..96fc84f 100644
--- a/src/Helpers/Arr.php
+++ b/src/Helpers/Arr.php
@@ -8,7 +8,7 @@
  *
  * @author Andrey Helldar <helldar@dragon-code.pro>
  *
- * @copyright 2024 Andrey Helldar
+ * @copyright 2025 Andrey Helldar
  *
  * @license MIT
  *
@@ -154,7 +154,7 @@ public function sortByKeys(array|ArrayObject $array, array $sorter): array
     {
         $sorter = array_intersect($sorter, array_keys($array));
 
-        return array_merge(array_flip($sorter), $array);
+        return $this->merge(array_flip($sorter), $array);
     }
 
     /**
@@ -542,7 +542,7 @@ public function flattenKeys(mixed $array, string $delimiter = '.', ?string $pref
             if (is_array($value)) {
                 $values = $this->flattenKeys($value, $delimiter, $new_key);
 
-                $result = array_merge($result, $values);
+                $result = $this->merge($result, $values);
 
                 continue;
             }
diff --git a/tests/Unit/Helpers/Arr/FlattenKeysTest.php b/tests/Unit/Helpers/Arr/FlattenKeysTest.php
index 0fb7171..9299147 100644
--- a/tests/Unit/Helpers/Arr/FlattenKeysTest.php
+++ b/tests/Unit/Helpers/Arr/FlattenKeysTest.php
@@ -8,7 +8,7 @@
  *
  * @author Andrey Helldar <helldar@dragon-code.pro>
  *
- * @copyright 2024 Andrey Helldar
+ * @copyright 2025 Andrey Helldar
  *
  * @license MIT
  *
@@ -155,4 +155,23 @@ public function testNested()
 
         $this->assertEquals($expected, Arr::flattenKeys($array));
     }
+
+    public function testMixedKeyTypes()
+    {
+        $array = [
+            404   => 'Foo',
+            '500' => 'Bar',
+            'baz' => 'Baz',
+            'qwe' => ['rty' => 'Qwerty'],
+        ];
+
+        $expected = [
+            '404'     => 'Foo',
+            '500'     => 'Bar',
+            'baz'     => 'Baz',
+            'qwe.rty' => 'Qwerty',
+        ];
+
+        $this->assertEquals($expected, Arr::flattenKeys($array));
+    }
 }