diff --git a/smoke/venv.sh b/smoke/venv.sh
index b20291f..df58d21 100755
--- a/smoke/venv.sh
+++ b/smoke/venv.sh
@@ -11,7 +11,10 @@ rm -rf venv .tox __pycache__ .pytest* test_*.py *.pyx *.c *.so || :
 $PYTHON -m venv venv
 
 # and activate it
+# unset variables on 3.5, it's known
+set +u
 source venv/bin/activate
+set -u
 
 # run python in it
 python -c 'import sys; print(sys.version)' | head -n1 | grep $VERSION