--- a/cubicweb/multipart.py	Wed Apr 10 17:59:17 2019 +0000
+++ b/cubicweb/multipart.py	Thu Apr 18 04:34:34 2019 +0000
@@ -101,10 +101,10 @@
 ##############################################################################
 
 _special = re.escape('()<>@,;:\\"/[]?={} \t')
-_re_special = re.compile('[%s]' % _special)
+_re_special = re.compile(r'[%s]' % _special)
 _qstr = '"(?:\\\\.|[^"])*"' # Quoted string
 _value = '(?:[^%s]+|%s)' % (_special, _qstr) # Save or quoted string
-_option = '(?:;|^)\s*([^%s]+)\s*=\s*(%s)' % (_special, _value)
+_option = r'(?:;|^)\s*([^%s]+)\s*=\s*(%s)' % (_special, _value)
 _re_option = re.compile(_option) # key=value part of an Content-Type like header
 
 def header_quote(val):