diff --git a/dav_base/emails.py b/dav_base/emails.py
index 023c109..b5b8d78 100644
--- a/dav_base/emails.py
+++ b/dav_base/emails.py
@@ -26,7 +26,7 @@ class AbstractMail(object):
 
     def _get_template(self):
         if not self._template_name:
-            raise ImproperlyConfigured('%s._template_name ist not set.', self.__class__.__name__)
+            raise ImproperlyConfigured('%s._template_name ist not set.' % self.__class__.__name__)
         return get_template(self._template_name, using='PLAINTEXT')
 
     def _get_context_data(self, extra_context=None):