--- a/python/mozbuild/mozbuild/shellutil.py
+++ b/python/mozbuild/mozbuild/shellutil.py
@@ -36,17 +36,17 @@ DOUBLY_QUOTED_TOKENS_RE = _tokens2re(
   special='\$',
   backslashed=r'\\[^\\"]',
 )
 
 ESCAPED_NEWLINES_RE = re.compile(r'\\\n')
 
 # This regexp contains the same characters as all those listed in
 # UNQUOTED_TOKENS_RE. Please keep in sync.
-SHELL_QUOTE_RE = re.compile('[\\\t\r\n \'\"#<>&|`~(){}$;\*\?]')
+SHELL_QUOTE_RE = re.compile(r'[\\\t\r\n \'\"#<>&|`~(){}$;\*\?]')
 
 
 class MetaCharacterException(Exception):
     def __init__(self, char):
         self.char = char
 
 
 class _ClineSplitter(object):