diff --git a/python/triqs_dft_tools/converters/plovasp/vaspio.py b/python/triqs_dft_tools/converters/plovasp/vaspio.py
index 02c6f67e..7d5e55ec 100644
--- a/python/triqs_dft_tools/converters/plovasp/vaspio.py
+++ b/python/triqs_dft_tools/converters/plovasp/vaspio.py
@@ -39,6 +39,7 @@ r"""
 import logging
 import numpy as np
 import re
+import os
 from h5 import HDFArchive
 
 log = logging.getLogger('plovasp.vaspio')