diff --git a/src/calibre/library/custom_columns.py b/src/calibre/library/custom_columns.py
index 535b8cfb72..90af46cc42 100644
--- a/src/calibre/library/custom_columns.py
+++ b/src/calibre/library/custom_columns.py
@@ -257,7 +257,7 @@ class CustomColumns(object):
                             'SELECT id FROM %s WHERE value=?'%table, (ex,), all=False)
                     if ex != x:
                         self.conn.execute(
-                                'UPDATE %s SET value=? WHERE id=?', (x, xid))
+                                'UPDATE %s SET value=? WHERE id=?'%table, (x, xid))
                 else:
                     xid = self.conn.execute(
                             'INSERT INTO %s(value) VALUES(?)'%table, (x,)).lastrowid
diff --git a/src/calibre/library/server/opds.py b/src/calibre/library/server/opds.py
index 86fae8bae8..dd1e2d0bb0 100644
--- a/src/calibre/library/server/opds.py
+++ b/src/calibre/library/server/opds.py
@@ -322,9 +322,17 @@ class OPDSServer(object):
             return self.get_opds_all_books(which, page_url, up_url,
                     version=version, offset=offset)
         elif type_ == 'N':
-            return self.get_opds_navcatalog(which)
+            return self.get_opds_navcatalog(which, version=version, offset=offset)
         raise cherrypy.HTTPError(404, 'Not found')
 
+    def get_opds_navcatalog(self, which, version=0, offset=0):
+        categories = self.categories_cache(
+                self.get_opds_allowed_ids_for_version(version))
+        if which not in categories:
+            raise cherrypy.HTTPError(404, 'Category %r not found'%which)
+
+
+
     def opds(self, version=0):
         version = int(version)
         if version not in BASE_HREFS: