diff --git a/hnn/qt_psd.py b/hnn/qt_psd.py
index d27f7fb2..83622e98 100644
--- a/hnn/qt_psd.py
+++ b/hnn/qt_psd.py
@@ -1,4 +1,5 @@
 import os
+import sys
 from math import sqrt
 from copy import deepcopy