diff --git a/pre_commit_hooks/xml_format.py b/pre_commit_hooks/xml_format.py
index 44f6442..855f4cf 100644
--- a/pre_commit_hooks/xml_format.py
+++ b/pre_commit_hooks/xml_format.py
@@ -1,11 +1,12 @@
 #!C:/miniconda/envs/plc-pre-commit/python.exe
 
 import argparse
-
 from lxml import etree
 
+TAB_WIDTH = 2
+
 
-def fix_file(filename):
+def fix_file(filename, tab_width=TAB_WIDTH):
     # lxml throws encoding errors unless we work in binary mode
     with open(filename, 'rb') as fd:
         original_xml = fd.read()
@@ -14,6 +15,7 @@ def fix_file(filename):
     # xmllint is cross-platform but pre-commit does not help us set it up
     xml_parser = etree.XMLParser(remove_blank_text=True)
     parse_tree = etree.XML(original_xml, parser=xml_parser).getroottree()
+    etree.indent(parse_tree, space=" " * tab_width)
     new_xml = etree.tostring(parse_tree,
                              pretty_print=True,
                              xml_declaration=True,
@@ -34,6 +36,7 @@ def main(args=None):
     if args is None:
         parser = argparse.ArgumentParser()
         parser.add_argument('filenames', nargs='*')
+        parser.add_argument('--tab-width', type=int, default=TAB_WIDTH)
         args = parser.parse_args()
     try:
         for filename in args.filenames: