diff --git a/code/heat_capacity.py b/code/heat_capacity.py
index ebd054fa05064dc9df0188352e1cf4de9514241a..f361f36016d71e4e2aae0fa962bd6492f7de2724 100644
--- a/code/heat_capacity.py
+++ b/code/heat_capacity.py
@@ -1,3 +1,5 @@
+import os
+
 import matplotlib
 matplotlib.use('agg')
 from matplotlib import pyplot