diff --git a/tests/playground/rbmap.library.lean b/tests/playground/rbmap.library.lean
index f91e97a051..2c845d006f 100644
--- a/tests/playground/rbmap.library.lean
+++ b/tests/playground/rbmap.library.lean
@@ -1,4 +1,4 @@
-@[reducible] def Map : Type := RBMap Nat Bool (<)
+@[reducible] def Map : Type := RBMap Nat Bool (λ a b, a < b)
 
 def mkMapAux : Nat → Map → Map
 | 0 m := m