diff --git a/pillar/api/eve_settings.py b/pillar/api/eve_settings.py
index e128c2e1..69da8704 100644
--- a/pillar/api/eve_settings.py
+++ b/pillar/api/eve_settings.py
@@ -623,7 +623,16 @@ projects_schema = {
     'permissions': {
         'type': 'dict',
         'schema': permissions_embedded_schema
-    }
+    },
+
+    # 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,
+    },
 }
 
 activities_subscriptions_schema = {