diff --git a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/DefaultArgumentStubGenerator.kt b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/DefaultArgumentStubGenerator.kt
index 4eefcd9fac0..719d3a4fff4 100644
--- a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/DefaultArgumentStubGenerator.kt
+++ b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/DefaultArgumentStubGenerator.kt
@@ -442,7 +442,7 @@ private fun IrFunction.generateDefaultsFunctionImpl(
         syntheticParameters += newFunction.valueParameter(
             syntheticParameters.last().index + 1,
             kConstructorMarkerName,
-            context.ir.symbols.defaultConstructorMarker.owner.defaultType
+            context.ir.symbols.defaultConstructorMarker.owner.defaultType.makeNullable()
         )
     } else if (context.ir.shouldGenerateHandlerParameterForDefaultBodyFun()) {
         syntheticParameters += newFunction.valueParameter(