diff --git a/tailbone/app.py b/tailbone/app.py
index 810d502c..44d9976f 100644
--- a/tailbone/app.py
+++ b/tailbone/app.py
@@ -2,7 +2,7 @@
 ################################################################################
 #
 #  Rattail -- Retail Software Framework
-#  Copyright © 2010-2018 Lance Edgar
+#  Copyright © 2010-2020 Lance Edgar
 #
 #  This file is part of Rattail.
 #
@@ -29,10 +29,11 @@ from __future__ import unicode_literals, absolute_import
 import os
 import warnings
 
+import six
 import sqlalchemy as sa
 from sqlalchemy.orm import sessionmaker, scoped_session
 
-from rattail.config import make_config
+from rattail.config import make_config, parse_list
 from rattail.exceptions import ConfigurationError
 from rattail.db.types import GPCType
 
@@ -161,8 +162,13 @@ def establish_theme(settings):
     theme = get_effective_theme(rattail_config)
     settings['tailbone.theme'] = theme
 
+    directories = settings['mako.directories']
+    if isinstance(directories, six.string_types):
+        directories = parse_list(directories)
+
     path = get_theme_template_path(rattail_config)
-    settings['mako.directories'].insert(0, path)
+    directories.insert(0, path)
+    settings['mako.directories'] = directories
 
 
 def configure_postgresql(pyramid_config):