diff --git a/numcodecs/tests/test_bitround.py b/numcodecs/tests/test_bitround.py
index 1e5fa701..05284bc5 100644
--- a/numcodecs/tests/test_bitround.py
+++ b/numcodecs/tests/test_bitround.py
@@ -78,3 +78,5 @@ def test_errors():
         BitRound(keepbits=99).encode(np.array([0], dtype="float32"))
     with pytest.raises(TypeError):
         BitRound(keepbits=10).encode(np.array([0]))
+    with pytest.raises(ValueError):
+        BitRound(-1)