diff --git a/core/descriptors/src/org/jetbrains/kotlin/builtins/functions/FunctionClassDescriptor.kt b/core/descriptors/src/org/jetbrains/kotlin/builtins/functions/FunctionClassDescriptor.kt
index 63eacb62f8c..a5662673326 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/builtins/functions/FunctionClassDescriptor.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/builtins/functions/FunctionClassDescriptor.kt
@@ -105,44 +105,29 @@ class FunctionClassDescriptor(
 
     private inner class FunctionTypeConstructor : AbstractClassTypeConstructor(storageManager) {
         override fun computeSupertypes(): Collection<KotlinType> {
-            val result = ArrayList<KotlinType>(2)
+            // For K{Suspend}Function{n}, add corresponding numbered {Suspend}Function{n} class, e.g. {Suspend}Function2 for K{Suspend}Function2
+            val supertypes = when (functionKind) {
+                Kind.Function -> // Function$N <: Function
+                    listOf(functionClassId)
+                Kind.KFunction -> // KFunction$N <: KFunction
+                    listOf(kFunctionClassId, ClassId(BUILT_INS_PACKAGE_FQ_NAME, Kind.Function.numberedClassName(arity)))
+                Kind.SuspendFunction -> // SuspendFunction$N<...> <: Function
+                    listOf(functionClassId)
+                Kind.KSuspendFunction -> // KSuspendFunction$N<...> <: KFunction
+                    listOf(kFunctionClassId, ClassId(COROUTINES_PACKAGE_FQ_NAME_RELEASE, Kind.SuspendFunction.numberedClassName(arity)))
+            }
 
-            fun add(id: ClassId) {
-                val moduleDescriptor = containingDeclaration.containingDeclaration
+            val moduleDescriptor = containingDeclaration.containingDeclaration
+            return supertypes.map { id ->
                 val descriptor = moduleDescriptor.findClassAcrossModuleDependencies(id) ?: error("Built-in class $id not found")
 
-                val typeConstructor = descriptor.typeConstructor
-
                 // Substitute all type parameters of the super class with our last type parameters
-                val arguments = parameters.takeLast(typeConstructor.parameters.size).map {
+                val arguments = parameters.takeLast(descriptor.typeConstructor.parameters.size).map {
                     TypeProjectionImpl(it.defaultType)
                 }
 
-                result.add(KotlinTypeFactory.simpleNotNullType(Annotations.EMPTY, descriptor, arguments))
-            }
-
-            when (functionKind) {
-                Kind.SuspendFunction -> // SuspendFunction$N<...> <: Function
-                    add(functionClassId)
-                Kind.KSuspendFunction -> // KSuspendFunction$N<...> <: KFunction
-                    add(kFunctionClassId)
-                Kind.Function -> // Function$N <: Function
-                    add(functionClassId)
-                Kind.KFunction -> // KFunction$N <: KFunction
-                    add(kFunctionClassId)
-            }
-
-            // For K{Suspend}Function{n}, add corresponding numbered {Suspend}Function{n} class, e.g. {Suspend}Function2 for K{Suspend}Function2
-            when (functionKind) {
-                Kind.KFunction ->
-                    add(ClassId(BUILT_INS_PACKAGE_FQ_NAME, Kind.Function.numberedClassName(arity)))
-                Kind.KSuspendFunction ->
-                    add(ClassId(COROUTINES_PACKAGE_FQ_NAME_RELEASE, Kind.SuspendFunction.numberedClassName(arity)))
-                else -> {
-                }
-            }
-
-            return result.toList()
+                KotlinTypeFactory.simpleNotNullType(Annotations.EMPTY, descriptor, arguments)
+            }.toList()
         }
 
         override fun getParameters() = this@FunctionClassDescriptor.parameters
@@ -159,7 +144,7 @@ class FunctionClassDescriptor(
     override fun toString() = name.asString()
 
     companion object {
-        val functionClassId = ClassId(BUILT_INS_PACKAGE_FQ_NAME, Name.identifier("Function"))
-        val kFunctionClassId = ClassId(KOTLIN_REFLECT_FQ_NAME, Name.identifier("KFunction"))
+        private val functionClassId = ClassId(BUILT_INS_PACKAGE_FQ_NAME, Name.identifier("Function"))
+        private val kFunctionClassId = ClassId(KOTLIN_REFLECT_FQ_NAME, Name.identifier("KFunction"))
     }
 }