diff --git a/sendgrid/helpers/mail/mail.py b/sendgrid/helpers/mail/mail.py
index e475fe76..2f23371b 100644
--- a/sendgrid/helpers/mail/mail.py
+++ b/sendgrid/helpers/mail/mail.py
@@ -464,7 +464,8 @@ def add_header(self, header):
         :param value: A Header object or a dict of header key/values
         :type value: Header, dict
         """
-        if header.personalization is not None:
+        if (isinstance(header, Header) and header.personalization is not None) or (
+                isinstance(header, dict) and header.get('personalization')):
             try:
                 personalization = \
                     self._personalizations[header.personalization]