diff --git a/mailing/models.py b/mailing/models.py
index 1a2067d..5f0d8d8 100644
--- a/mailing/models.py
+++ b/mailing/models.py
@@ -35,7 +35,7 @@ class MessageAuthor(models.Model):
 
     def __str__(self):
         author_class = self.author_type.model_class()
-        if author_class == get_user_model():
+        if self.author is not None and author_class == get_user_model():
             return self.author.get_full_name()
         else:
             return str(self.author)