diff --git a/python/ray/rllib/optimizers/aso_multi_gpu_learner.py b/python/ray/rllib/optimizers/aso_multi_gpu_learner.py
index 032dc9c69..a584be7e6 100644
--- a/python/ray/rllib/optimizers/aso_multi_gpu_learner.py
+++ b/python/ray/rllib/optimizers/aso_multi_gpu_learner.py
@@ -6,6 +6,7 @@ from __future__ import print_function
 
 import logging
 import threading
+import math
 
 from six.moves import queue