diff --git a/libraries/AP_Param/AP_Param.h b/libraries/AP_Param/AP_Param.h
index da78771ba0..78f063d4b1 100644
--- a/libraries/AP_Param/AP_Param.h
+++ b/libraries/AP_Param/AP_Param.h
@@ -93,6 +93,9 @@
 // an object
 #define AP_SUBGROUPINFO(element, name, idx, thisclazz, elclazz) { AP_PARAM_GROUP, idx, name, AP_VAROFFSET(thisclazz, element), { group_info : elclazz::var_info }, AP_PARAM_FLAG_NESTED_OFFSET }
 
+// declare a second parameter table for the same object
+#define AP_SUBGROUPEXTENSION(name, idx, clazz, vinfo) { AP_PARAM_GROUP, idx, name, 0, { group_info : clazz::vinfo }, AP_PARAM_FLAG_NESTED_OFFSET }
+
 // declare a pointer subgroup entry in a group var_info
 #define AP_SUBGROUPPTR(element, name, idx, thisclazz, elclazz) { AP_PARAM_GROUP, idx, name, AP_VAROFFSET(thisclazz, element), { group_info : elclazz::var_info }, AP_PARAM_FLAG_POINTER }