diff --git a/src/sage/combinat/finite_state_machine_generators.py b/src/sage/combinat/finite_state_machine_generators.py
index 2ba80f70e71..eb785aeb9b3 100644
--- a/src/sage/combinat/finite_state_machine_generators.py
+++ b/src/sage/combinat/finite_state_machine_generators.py
@@ -1223,7 +1223,7 @@ def parse_equation(equation):
         def transition_function((carry, look_ahead), input):
             current = carry + input * base**look_ahead
             K = look_ahead + 1
-            R = current % 2**K
+            R = current % base**K
             rule = residues[K][R]
             if rule is not None:
                 n = (current - R) / base**K