diff --git a/doc/lua_api.txt b/doc/lua_api.txt
index 442937b..de364a5 100644
--- a/doc/lua_api.txt
+++ b/doc/lua_api.txt
@@ -456,6 +456,7 @@ Special groups
 - disable_jump: Player (and possibly other things) cannot jump from node
 - fall_damage_add_percent: damage speed = speed * (1 + value/100)
 - bouncy: value is bounce speed in percent
+- falling_node: if there is no walkable block under the node it will fall
 
 Known damage and digging time defining groups
 ----------------------------------------------