diff --git a/imbox/parser.py b/imbox/parser.py
index 6e25a34..9ad1314 100644
--- a/imbox/parser.py
+++ b/imbox/parser.py
@@ -33,7 +33,7 @@ def decode_mail_header(value, default_charset='us-ascii'):
         return str_decode(str_encode(value, default_charset, 'replace'), default_charset)
     else:
         for index, (text, charset) in enumerate(headers):
-            logger.debug("Mail header no. {}: {} encoding {}".format(index, str_decode(text, charset or 'utf-8'), charset))
+            logger.debug("Mail header no. {}: {} encoding {}".format(index, str_decode(text, charset or 'utf-8', 'replace'), charset))
             try:
                 headers[index] = str_decode(text, charset or default_charset,
                                             'replace')
diff --git a/tests/parser_tests.py b/tests/parser_tests.py
index 46baa70..73f8de0 100644
--- a/tests/parser_tests.py
+++ b/tests/parser_tests.py
@@ -336,6 +336,9 @@ class TestParser(unittest.TestCase):
         from_message_object = email.message_from_string("From: John Smith <johnsmith@gmail.com>")
         self.assertEqual([{'email': 'johnsmith@gmail.com', 'name': 'John Smith'}], get_mail_addresses(from_message_object, 'from'))
 
+        invalid_encoding_in_from_message_object = email.message_from_string("From: =?UTF-8?Q?C=E4cilia?= <caciliahxg827m@example.org>")
+        self.assertEqual([{'email': 'caciliahxg827m@example.org', 'name': 'C�cilia'}], get_mail_addresses(invalid_encoding_in_from_message_object, 'from'))
+
     def test_parse_email_with_policy(self):
         if not SMTP:
             return