diff --git a/server.py b/server.py
index 3256716..c18cd6d 100644
--- a/server.py
+++ b/server.py
@@ -75,7 +75,7 @@ def alter(partID):
             datasheet_filename = secure_filename(datasheet_file.filename)
             datasheet_file.save('/srv/datasheets/' + datasheet_filename)
         else:
-            datasheet_filename = ''
+            datasheet_filename = None
         r = db_engine.execute(s, block=request.form['block'],
                                  type=request.form['type'],
                                  partno=request.form['partno'],