diff --git a/Tests/test_tiff_ifdrational.py b/Tests/test_tiff_ifdrational.py
index e212ba64a..4fd5b8fbe 100644
--- a/Tests/test_tiff_ifdrational.py
+++ b/Tests/test_tiff_ifdrational.py
@@ -86,7 +86,7 @@ def test_ifd_rational_save(
         (0, 0, float("nan")),
     ],
 )
-def test_float_cast(numerator, denominator, expected_result):
+def test_float_cast(numerator: int, denominator: int, expected_result: float) -> None:
     value = float(IFDRational(numerator, denominator))
     if math.isnan(expected_result):
         assert value