diff --git a/src/caoscrawler/converters.py b/src/caoscrawler/converters.py
index 80c0b1f706e275a9876e01d8fbdf321528dd559f..39a6bf2b987cb68ffffd359923c255c8af54839f 100644
--- a/src/caoscrawler/converters.py
+++ b/src/caoscrawler/converters.py
@@ -36,7 +36,7 @@ from .structure_elements import (StructureElement, Directory, File, Dict, JSONFi
                                  DictFloatElement, DictDictElement,
                                  TextElement, DictTextElement, DictElement, DictListElement)
 from typing import Dict as Dict_t, List, Optional, Tuple, Union
-from abc import abstractmethod
+from abc import ABCMeta, abstractmethod
 from string import Template
 import yaml_header_tools
 
@@ -255,7 +255,7 @@ def create_records(values: GeneralStore,
     return keys_modified
 
 
-class Converter(object):
+class Converter(object, metaclass=ABCMeta):
     """
     Converters treat StructureElements contained in the hierarchical sturcture.
     """
diff --git a/src/caoscrawler/crawl.py b/src/caoscrawler/crawl.py
index d2758baaead7713aa9fedb8b9ad96163405cdf39..0704cee918f771bb01ec624b01aa529821a29edc 100644
--- a/src/caoscrawler/crawl.py
+++ b/src/caoscrawler/crawl.py
@@ -1117,6 +1117,7 @@ def parse_args():
                         help="The subtree of files below the given path will "
                         "be considered. Use '/' for everything.")
     parser.add_argument("-s", "--security-mode", choices=["retrieve", "insert", "update"],
+                        default="retrieve",
                         help="Determines whether entities may only be read from the server, or "
                         "whether inserts or even updates may be done.")
     parser.add_argument("-n", "--dry-run", action="store_true",