diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -796,7 +796,7 @@
 
         # This logic is duplicated in doc/Makefile.
         sources = {f for f in os.listdir('mercurial/help')
-                   if re.search('[0-9]\.txt$', f)}
+                   if re.search(r'[0-9]\.txt$', f)}
 
         # common.txt is a one-off.
         gentxt('common')