diff --git a/test/test_model/test_c6.py b/test/test_model/test_c6.py
index f49ad22..f27092d 100644
--- a/test/test_model/test_c6.py
+++ b/test/test_model/test_c6.py
@@ -15,6 +15,8 @@
 """
 Test C6 coefficients.
 """
+from __future__ import annotations
+
 import pytest
 import torch
 from tad_mctc.autograd import dgradcheck, dgradgradcheck