diff --git a/calsocial/__init__.py b/calsocial/__init__.py
index d03e802..96b989b 100644
--- a/calsocial/__init__.py
+++ b/calsocial/__init__.py
@@ -72,7 +72,7 @@ class CalendarSocialApp(Flask, RoutedMixin):
 
         self._timezone = None
 
-        config_name = os.environ.get('ENV', config or 'development')
+        config_name = os.environ.get('FLASK_ENV', config or 'development')
         self.config.from_pyfile(f'config_{config_name}.py', True)
         # Make sure we look up users both by their usernames and email addresses
         self.config['SECURITY_USER_IDENTITY_ATTRIBUTES'] = ('username', 'email')