diff --git a/smoke/venv.sh b/smoke/venv.sh
index 5b166dd..a557489 100755
--- a/smoke/venv.sh
+++ b/smoke/venv.sh
@@ -31,7 +31,7 @@ python -c 'import sys; print(sys.version)' | head -n1 | grep $VERSION
 
 # install packages with pip
 if [ "$VERSION" == "2.6" ]; then
-    pip install pytest Cython
+    pip install pytest "Cython<28"
 else
     python -m pip install pytest Cython
 fi