diff --git a/lib/gears/timer.lua b/lib/gears/timer.lua
index 2cc2bbb5..c01b49f4 100644
--- a/lib/gears/timer.lua
+++ b/lib/gears/timer.lua
@@ -158,7 +158,7 @@ function timer.new(args)
     args = args or {}
     local ret = object()
 
-    ret.data = { timeout = 0 }
+    ret.data = { timeout = 0 } --TODO v5 rename to ._private
     setmetatable(ret, timer_instance_mt)
 
     for k, v in pairs(args) do