diff --git a/fitsio/fitslib.py b/fitsio/fitslib.py
index 01ae48b..5e6dc88 100644
--- a/fitsio/fitslib.py
+++ b/fitsio/fitslib.py
@@ -1874,7 +1874,7 @@ def get_dither_seed(dither_seed):
         seed_out = 0
     else:
         # must fit in an int
-        seed_out = numpy.int32(dither_seed).clip(min=-1)
+        seed_out = numpy.int32(dither_seed)
 
     if seed_out > 10_000:
         raise ValueError(
diff --git a/fitsio/tests/test_image_compression.py b/fitsio/tests/test_image_compression.py
index 26aef3d..b355c53 100644
--- a/fitsio/tests/test_image_compression.py
+++ b/fitsio/tests/test_image_compression.py
@@ -266,7 +266,8 @@ def test_compressed_seed(compress, seed_type, use_fits_object, dtype):
         dither_seed2 = 'checksum'
     elif seed_type == 'checksum_int':
         dither_seed1 = -1
-        dither_seed2 = -1
+        # any negative means use checksum
+        dither_seed2 = -3
 
     with tempfile.TemporaryDirectory() as tmpdir:
         fname1 = os.path.join(tmpdir, 'test1.fits')