diff --git a/mhcflurry/parallelism.py b/mhcflurry/parallelism.py
index 6de51e099f8ce644c31324ec210d55de960b3f16..53a1ae86dfa05b2ecd0a71c2d33c248b995f8811 100644
--- a/mhcflurry/parallelism.py
+++ b/mhcflurry/parallelism.py
@@ -1,5 +1,4 @@
 import logging
-from six import PY2
 from concurrent import futures
 
 DEFAULT_BACKEND = None