diff --git a/ckanext/odsh/lib/uploader.py b/ckanext/odsh/lib/uploader.py
index b71cfe52fce88c8917aa832524cdaa35ffee39ff..ab89260a54cada77b3de43f81834e2ab600bd67f 100644
--- a/ckanext/odsh/lib/uploader.py
+++ b/ckanext/odsh/lib/uploader.py
@@ -29,6 +29,7 @@ def _raise_validation_error_if_virus_found(filename, upload_file):
 
 
 def calculate_hash(upload_file):
+    upload_file.seek(0)
     hash_md5 = hashlib.md5()
     for chunk in iter(lambda: upload_file.read(4096), b""):
             hash_md5.update(chunk)