diff --git a/lib/tempest b/lib/tempest
index 96c9ced..7d0a982 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -107,7 +107,7 @@
 function image_size_in_gib {
     local size
     size=$(openstack image show $1 -c size -f value)
-    echo $size | python -c "import math; import six; print(int(math.ceil(float(int(six.moves.input()) / 1024.0 ** 3))))"
+    echo $size | python3 -c "import math; print(int(math.ceil(float(int(input()) / 1024.0 ** 3))))"
 }
 
 # configure_tempest() - Set config files, create data dirs, etc