diff --git a/simgear/structure/subsystem_mgr.hxx b/simgear/structure/subsystem_mgr.hxx
index 87654d9c..02332056 100644
--- a/simgear/structure/subsystem_mgr.hxx
+++ b/simgear/structure/subsystem_mgr.hxx
@@ -384,6 +384,8 @@ public:
         INIT = 0,
         GENERAL,
         FDM,  ///< flight model, autopilot, instruments that run coupled
+        POST_FDM,   ///< certain subsystems depend on FDM data
+        DISPLAY,    ///< view, camera, rendering updates
         MAX_GROUPS
     };