diff --git a/docs/sphinx/hxtool.py b/docs/sphinx/hxtool.py
index fb0649a3d5..9f6b9d87dc 100644
--- a/docs/sphinx/hxtool.py
+++ b/docs/sphinx/hxtool.py
@@ -49,7 +49,7 @@ def serror(file, lnum, errtext):
 
 def parse_directive(line):
     """Return first word of line, if any"""
-    return re.split('\W', line)[0]
+    return re.split(r'\W', line)[0]
 
 def parse_defheading(file, lnum, line):
     """Handle a DEFHEADING directive"""