diff --git a/test/utils/test_utils.py b/test/utils/test_utils.py
index d8b9cec..eb87951 100644
--- a/test/utils/test_utils.py
+++ b/test/utils/test_utils.py
@@ -110,7 +110,7 @@ def elaborate(self, platform):
         return m
 
 
-@pytest.mark.parametrize("size", range(1, 65))
+@pytest.mark.parametrize("size", [1,2,3,4,5,6,7,8,9,15,16,17,31,32,33,63,64,65,97,98,127,128])
 class TestCountLeadingZeros(TestCaseWithSimulator):
     @pytest.fixture(scope="function", autouse=True)
     def setup_fixture(self, size):
@@ -156,7 +156,7 @@ def elaborate(self, platform):
         return m
 
 
-@pytest.mark.parametrize("size", range(1, 65))
+@pytest.mark.parametrize("size", [1,2,3,4,5,6,7,8,9,15,16,17,31,32,33,63,64,65,97,98,127,128])
 class TestCountTrailingZeros(TestCaseWithSimulator):
     @pytest.fixture(scope="function", autouse=True)
     def setup_fixture(self, size):