diff --git a/frappe/app.py b/frappe/app.py
index b4c6c5b8aa..11ea4ba036 100644
--- a/frappe/app.py
+++ b/frappe/app.py
@@ -219,11 +219,11 @@ def serve(port=8000, profile=False, site=None, sites_path='.'):
 
 	if not os.environ.get('NO_STATICS'):
 		application = SharedDataMiddleware(application, {
-			'/assets': os.path.join(sites_path, 'assets'),
+			str('/assets'): str(os.path.join(sites_path, 'assets'))
 		})
 
 		application = StaticDataMiddleware(application, {
-			'/files': os.path.abspath(sites_path)
+			str('/files'): str(os.path.abspath(sites_path))
 		})
 
 	application.debug = True