diff --git a/src/dcmstack/extract.py b/src/dcmstack/extract.py
index 40fd911..4fbe60d 100644
--- a/src/dcmstack/extract.py
+++ b/src/dcmstack/extract.py
@@ -6,6 +6,7 @@
 import dicom
 from dicom.datadict import keyword_for_tag
 from nibabel.nicom import csareader
+import sys
 from .dcmstack import DicomStack
 try:
     from collections import OrderedDict