diff --git a/src/ReactiveTools.jl b/src/ReactiveTools.jl
index 79d2e148..48eac328 100644
--- a/src/ReactiveTools.jl
+++ b/src/ReactiveTools.jl
@@ -960,8 +960,10 @@ macro onbutton(location, var, expr)
   known_vars = vcat(known_reactive_vars, known_non_reactive_vars)
   var = fieldnames_to_fields(var, known_vars)
 
+  expr, used_vars = mask(expr, known_vars)
+
   expr = fieldnames_to_fields(expr, known_non_reactive_vars)
-  expr = fieldnames_to_fieldcontent(expr, known_reactive_vars, known_reactive_vars)
+  expr = fieldnames_to_fieldcontent(expr, known_reactive_vars)
   expr = unmask(expr, known_vars)
 
   ex = :(onbutton($var) do