diff --git a/docs/index.rst b/docs/index.rst
index c5805cb..1145b6b 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -201,6 +201,9 @@ To group settings together you can define fieldsets. Here's an example:
             'General Options': ('SITE_NAME', 'SITE_DESCRIPTION'),
             'Theme Options': ('THEME',),
         }
+        
+.. note:: CONSTANCE_CONFIG_FIELDSETS must contain all fields from CONSTANCE_CONFIG
+
 .. image:: screenshot3.png
 
 Usage