diff --git a/tests/01_int.py b/tests/01_int.py
index 79089b2d..2f3806a8 100644
--- a/tests/01_int.py
+++ b/tests/01_int.py
@@ -57,6 +57,10 @@ assert (1).bit_length() == 1
 assert (2).bit_length() == 2
 assert (3).bit_length() == 2
 
+assert (-1).bit_length() == 1
+assert (-2).bit_length() == 2
+assert (-3).bit_length() == 2
+
 # test int()
 assert int() == 0
 assert int(True) == 1