diff --git a/tabellio/pcfdb/sync.py b/tabellio/pcfdb/sync.py
index 92bcaab..2ab1e4d 100644
--- a/tabellio/pcfdb/sync.py
+++ b/tabellio/pcfdb/sync.py
@@ -762,7 +762,10 @@ class SyncFromPcfDbView(BrowserView):
             object.session = sess
             object.date = date
             object.no = no
-            object.nodoc = nodoc
+            if nodoc:
+                object.nodoc = str(nodoc)
+            else:
+                object.nodoc = None
             object.doctype = doctype
             object.file_image_id = image_id
             object.topics = topics