diff --git a/src/shamira/gf256.py b/src/shamira/gf256.py
--- a/src/shamira/gf256.py
+++ b/src/shamira/gf256.py
@@ -2,9 +2,11 @@
 
 """Arithmetic operations on Galois Field 2**8. See https://en.wikipedia.org/wiki/Finite_field_arithmetic"""
 
-from functools import reduce, cache
+from functools import reduce
 import operator
 
+from .util import cache
+
 
 def _gfmul(a, b):
 	"""Basic multiplication. Russian peasant algorithm."""