diff --git a/tardis/base.py b/tardis/base.py
index 2c091cd7805..71b10229dc1 100644
--- a/tardis/base.py
+++ b/tardis/base.py
@@ -23,6 +23,7 @@ def run_tardis(config, atom_data=None):
 
     from tardis.io import config_reader
     from tardis import model, simulation, atomic
+    import os
 
     try:
         config_dict = yaml.load(open(config))