diff --git a/cirq-core/cirq/experiments/single_qubit_readout_calibration.py b/cirq-core/cirq/experiments/single_qubit_readout_calibration.py
index 003ab34f365..3090c485e16 100644
--- a/cirq-core/cirq/experiments/single_qubit_readout_calibration.py
+++ b/cirq-core/cirq/experiments/single_qubit_readout_calibration.py
@@ -14,7 +14,7 @@
 """Single qubit readout experiments using parallel or isolated statistics."""
 import dataclasses
 import time
-from typing import Any, Dict, Iterable, List, Optional, TYPE_CHECKING
+from typing import Any, Dict, Iterable, List, Optional, TYPE_CHECKING, cast
 
 import sympy
 import numpy as np