diff --git a/pisi/specfile.py b/pisi/specfile.py
index 2089207f..0ec570ef 100644
--- a/pisi/specfile.py
+++ b/pisi/specfile.py
@@ -148,7 +148,7 @@ class Source:
     t_Summary = [autoxml.LocalText, autoxml.mandatory]
     t_Description = [autoxml.LocalText, autoxml.mandatory]
     t_IsA = [ [autoxml.String], autoxml.mandatory]
-    t_PartOf = [autoxml.String, autoxml.mandatory]
+    t_PartOf = [autoxml.String, autoxml.optional]
     t_Icon = [ autoxml.String, autoxml.optional]
     t_License = [ [autoxml.String], autoxml.mandatory]
     t_Archive = [Archive, autoxml.mandatory ]
diff --git a/tools/cat-source-repo.py b/tools/cat-source-repo.py
index 8e35e129..cac61d06 100755
--- a/tools/cat-source-repo.py
+++ b/tools/cat-source-repo.py
@@ -1,4 +1,6 @@
 #! /usr/bin/python
+# a simple tool to list stuff in source repository
+# author: exa
 
 import sys
 import os
@@ -11,7 +13,7 @@ import pisi.context as ctx
 import pisi.util
 
 options = pisi.config.Options()
-if len(sys.argv)>2:
+if len(sys.argv) > 2:
     options.destdir=sys.argv[2]
 else:
     options.destdir = '/'