diff --git a/pillar/api/eve_settings.py b/pillar/api/eve_settings.py
index b7c54cf6..3d67755e 100644
--- a/pillar/api/eve_settings.py
+++ b/pillar/api/eve_settings.py
@@ -127,7 +127,16 @@ users_schema = {
                 'schema': {'type': 'string'}
             }
         }
-    }
+    },
+
+    # Properties defined by extensions. Extensions should use their name
+    # (see the PillarExtension.name property) as the key, and are free to
+    # use whatever they want as value (but we suggest a dict for future
+    # extendability).
+    'extension_props': {
+        'type': 'dict',
+        'required': False,
+    },
 }
 
 organizations_schema = {