diff --git a/machine-learning/app/sessions/rknn/rknnpool.py b/machine-learning/app/sessions/rknn/rknnpool.py
index 35927243f9..c1342b6979 100644
--- a/machine-learning/app/sessions/rknn/rknnpool.py
+++ b/machine-learning/app/sessions/rknn/rknnpool.py
@@ -4,6 +4,7 @@
 from concurrent.futures import Future, ThreadPoolExecutor
 from pathlib import Path
 from queue import Queue
+from typing import Callable
 
 import numpy as np
 from numpy.typing import NDArray