--- a/pyramid_cubicweb/__init__.py	Fri Jun 03 17:58:43 2016 +0200
+++ b/pyramid_cubicweb/__init__.py	Thu Jun 16 16:25:32 2016 +0200
@@ -136,7 +136,7 @@
 
     """
     if instance_name is None:
-        instance_name = os.environ.get('CW_INSTANCE')
+        instance_name = os.environ['CW_INSTANCE']
     if debug is None:
         debug = 'CW_DEBUG' in os.environ