diff --git a/tests/test_formatters.py b/tests/test_formatters.py
index e87a017..6a0515f 100644
--- a/tests/test_formatters.py
+++ b/tests/test_formatters.py
@@ -56,7 +56,7 @@ class TestDateFormat:
         assert r[0, 1].strftime("%H:%M:%S") == "11:11:11"
         assert isinstance(r[0, 2], datetime.date) is True
         assert r[0, 2].strftime("%d/%m/%y %H:%M:%S") == "25/12/14 11:11:11"
-        assert isinstance(r[0, 2], datetime.timedelta)
+        assert isinstance(r[0, 3], datetime.timedelta)
         assert r[0, 1].strftime("%H:%M:%S") == "3:30:20"
         os.unlink(excel_filename)