diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt
index 8608936f2dc..cbf4a2ad688 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt
@@ -59,7 +59,7 @@ interface IrTypeSystemContext : TypeSystemContext, TypeSystemCommonSuperTypesCon
 
     override fun SimpleTypeMarker.asDefinitelyNotNullType(): DefinitelyNotNullTypeMarker? = null
 
-    override fun SimpleTypeMarker.isMarkedNullable(): Boolean = (this as IrSimpleType).isMarkedNullable()
+    override fun SimpleTypeMarker.isMarkedNullable(): Boolean = (this as IrSimpleType).hasQuestionMark
 
     override fun SimpleTypeMarker.withNullability(nullable: Boolean): SimpleTypeMarker {
         val simpleType = this as IrSimpleType