diff --git a/themis/importexport/sync.py b/themis/importexport/sync.py
index 46135b2..03be64d 100644
--- a/themis/importexport/sync.py
+++ b/themis/importexport/sync.py
@@ -383,6 +383,7 @@ class SyncFromThemis(UtilityView):
                 authors_intids = [self.get_author_intid(x) for x in authors_v]
                 if None in authors_intids:
                     log.warn('unknown error in doc %s' % object.id)
+                authors_intids = [x for x in authors_intids if x is not None]
                 object.authors = self.create_relation_value_list_if_needed(
                         object.authors, authors_intids)
                 object.author_is_government = False