diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index aae819880ee2..abe3810fb0ab 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -2508,11 +2508,11 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
         !(tp2 <:< tp1)
         && (provablyDisjoint(tp1, tp2.tp2) || provablyDisjoint(tp1, tp2.tp1))
       case (tp1: TypeProxy, tp2: TypeProxy) =>
-        provablyDisjoint(tp1.underlying, tp2) || provablyDisjoint(tp1, tp2.underlying)
+        provablyDisjoint(tp1.superType, tp2) || provablyDisjoint(tp1, tp2.superType)
       case (tp1: TypeProxy, _) =>
-        provablyDisjoint(tp1.underlying, tp2)
+        provablyDisjoint(tp1.superType, tp2)
       case (_, tp2: TypeProxy) =>
-        provablyDisjoint(tp1, tp2.underlying)
+        provablyDisjoint(tp1, tp2.superType)
       case _ =>
         false
     }
diff --git a/tests/run-macros/tasty-simplified.check b/tests/run-macros/tasty-simplified.check
index ae73a625ac58..55e725e10f17 100644
--- a/tests/run-macros/tasty-simplified.check
+++ b/tests/run-macros/tasty-simplified.check
@@ -1,4 +1,4 @@
-Functor[[A >: scala.Nothing <: scala.Any] => scala.collection.immutable.List[A]]
+Functor[Const[scala.collection.immutable.List[Dummy]]]
 Functor[Const[scala.Int]]
-Functor[Id]
-Functor[[A >: scala.Nothing <: scala.Any] => scala.Option[A]]
+Functor[Const[Dummy]]
+Functor[Const[scala.Option[Dummy]]]