diff --git a/Tests/test_imageops.py b/Tests/test_imageops.py
index 0b0bd1295..12db93a22 100644
--- a/Tests/test_imageops.py
+++ b/Tests/test_imageops.py
@@ -606,7 +606,7 @@ def test_autocontrast_preserve_one_color(color: tuple[int, int, int]) -> None:
     assert_image_equal(img, out)
 
 
-def test_dither_primary_returns_image():
+def test_dither_primary_returns_image() -> None:
     im = Image.new("RGB", (4, 4), (128, 128, 128))
     out = ImageOps.dither_primary(im)