diff --git a/tools/new_source.py b/tools/new_source.py
index 2985cb0..49e1ae7 100644
--- a/tools/new_source.py
+++ b/tools/new_source.py
@@ -77,7 +77,7 @@ def create_header() -> None:
 
     _logger.info('Generating header at %s.', str(_header_path))
 
-    guard = '_'.join(_header_path.with_suffix('').parts[1:]).upper()
+    guard = '_'.join((*_header_path.parts[1:], 'INCLUDED')).upper().replace('.', '_')
     generate_file(_HEADER_TEMPLATE_NAME, _header_path, {
         'guard': guard,
         'namespace': _namespace