diff --git a/hgext/schemes.py b/hgext/schemes.py
--- a/hgext/schemes.py
+++ b/hgext/schemes.py
@@ -135,7 +135,7 @@ schemes = {
 }
 
 
-def _check_drive_letter(scheme):
+def _check_drive_letter(scheme: bytes) -> None:
     """check if a scheme conflict with a Windows drive letter"""
     if (
         pycompat.iswindows
@@ -152,7 +152,7 @@ def extsetup(ui):
     schemes.update(dict(ui.configitems(b'schemes')))
     t = templater.engine(templater.parse)
     for scheme, url in schemes.items():
-        _check_drive_letter(schemes)
+        _check_drive_letter(scheme)
         url_scheme = urlutil.url(url).scheme
         if url_scheme in hg.peer_schemes:
             hg.peer_schemes[scheme] = ShortRepository(url, scheme, t)