diff --git a/sendgrid/helpers/mail/validators.py b/sendgrid/helpers/mail/validators.py
index 816ec71a4..4ca49a08a 100644
--- a/sendgrid/helpers/mail/validators.py
+++ b/sendgrid/helpers/mail/validators.py
@@ -25,7 +25,7 @@ def __init__(self, regex_strings=None, use_default=True):
                 self.regexes.add(re.compile(regex_string))
 
         if use_default:
-            default_regex_string = 'SG\.[0-9a-zA-Z]+\.[0-9a-zA-Z]+'
+            default_regex_string = r'SG\.[0-9a-zA-Z]+\.[0-9a-zA-Z]+'
             self.regexes.add(re.compile(default_regex_string))
 
     def validate_message_dict(self, request_body):