diff --git a/source/python/mods/tools.py b/source/python/mods/tools.py
index b1e5c6073132132dc151a785ee8c0359be947491..070763b9923cb7a1f970c436d7c6c6fe854ff316 100644
--- a/source/python/mods/tools.py
+++ b/source/python/mods/tools.py
@@ -180,7 +180,7 @@ def get_cmdline_arguments():
 
     # this is only used by prepare_flexpart.py to rerun a postprocessing step
     parser.add_argument("--ppid", dest="ppid",
-                        type=none_or_int, default=None,
+                        type=none_or_str, default=None,
                         help="specify parent process id for \
                         rerun of prepare_flexpart")