diff --git a/src/sage/algebras/fusion_rings/f_matrix.py b/src/sage/algebras/fusion_rings/f_matrix.py
index 7043f2f3491..7bc57ebbaee 100644
--- a/src/sage/algebras/fusion_rings/f_matrix.py
+++ b/src/sage/algebras/fusion_rings/f_matrix.py
@@ -889,7 +889,7 @@ def _get_known_nonz(self):
              100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100)
         """
         nonz = {idx: 100 for idx in self._singles}
-        for idx in self._ks:
+        for idx, _ in self._ks.items():
             nonz[idx] = 100
         return ETuple(nonz, self._poly_ring.ngens())