diff --git a/pytket/extensions/qiskit/qiskit_convert.py b/pytket/extensions/qiskit/qiskit_convert.py
index 6e22e6ad..ad206ccf 100644
--- a/pytket/extensions/qiskit/qiskit_convert.py
+++ b/pytket/extensions/qiskit/qiskit_convert.py
@@ -1062,11 +1062,9 @@ def get_avg_characterisation(
         dict[Node, list[list[float]]], characterisation["ReadoutErrors"]
     )
 
-    avg: Callable[[dict[Any, float]], float] = lambda xs: sum(
+    avg: Callable[[dict[Any, float]], float] = lambda xs: sum(  # noqa: E731
         xs.values()
-    ) / len(  # noqa: E731
-        xs
-    )
+    ) / len(xs)
     avg_mat: Callable[[list[list[float]]], float] = (  # noqa: E731
         lambda xs: (xs[0][1] + xs[1][0]) / 2.0
     )