diff --git a/src/shamira/fft.py b/src/shamira/fft.py
--- a/src/shamira/fft.py
+++ b/src/shamira/fft.py
@@ -3,8 +3,8 @@
 import math
 import cmath
 import itertools
-from functools import cache
 
+from .util import cache
 from .gf256 import gfmul, gfpow
 
 # divisors of 255 and their factors in natural numbers