diff --git a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/DeepCopyIrTreeWithSymbolsForFakeOverrides.kt b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/DeepCopyIrTreeWithSymbolsForFakeOverrides.kt
index c2fc5ede737..cd8e4bfb463 100644
--- a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/DeepCopyIrTreeWithSymbolsForFakeOverrides.kt
+++ b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/DeepCopyIrTreeWithSymbolsForFakeOverrides.kt
@@ -15,19 +15,13 @@ import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.ir.visitors.acceptVoid
 
 // This is basicly modelled after the inliner copier.
-class DeepCopyIrTreeWithSymbolsForFakeOverrides(
-    val typeArguments: Map<IrTypeParameterSymbol, IrType>,
-    val superType: IrType,
-    val parent: IrClass
-) {
+class DeepCopyIrTreeWithSymbolsForFakeOverrides(typeArguments: Map<IrTypeParameterSymbol, IrType>) {
 
-    fun copy(irElement: IrElement): IrElement {
+    fun copy(irElement: IrElement, parent: IrClass): IrElement {
         // Create new symbols.
         irElement.acceptVoid(symbolRemapper)
 
         // Make symbol remapper aware of the callsite's type arguments.
-        symbolRemapper.typeArguments = typeArguments
-
         // Copy IR.
         val result = irElement.transform(copier, data = null)
 
@@ -76,16 +70,12 @@ class DeepCopyIrTreeWithSymbolsForFakeOverrides(
         }
     }
 
-    private class FakeOverrideSymbolRemapperImpl(descriptorsRemapper: DescriptorsRemapper) :
+    private class FakeOverrideSymbolRemapperImpl(
+        private val typeArguments: Map<IrTypeParameterSymbol, IrType>,
+        descriptorsRemapper: DescriptorsRemapper
+    ) :
         DeepCopySymbolRemapper(descriptorsRemapper) {
 
-        var typeArguments = mapOf<IrTypeParameterSymbol, IrType>()
-            set(value) {
-                field = value.asSequence().associate {
-                    (getReferencedClassifier(it.key) as IrTypeParameterSymbol) to it.value
-                }
-            }
-
         override fun getReferencedClassifier(symbol: IrClassifierSymbol): IrClassifierSymbol {
             val result = super.getReferencedClassifier(symbol)
             if (result !is IrTypeParameterSymbol)
@@ -94,9 +84,8 @@ class DeepCopyIrTreeWithSymbolsForFakeOverrides(
         }
     }
 
-    private val symbolRemapper = FakeOverrideSymbolRemapperImpl(DescriptorsToIrRemapper)
-    private val copier =
-        FakeOverrideCopier(
+    private val symbolRemapper = FakeOverrideSymbolRemapperImpl(typeArguments, DescriptorsToIrRemapper)
+    private val copier = FakeOverrideCopier(
             symbolRemapper,
             FakeOverrideTypeRemapper(symbolRemapper, typeArguments),
             SymbolRenamer.DEFAULT
diff --git a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/FakeOverrides.kt b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/FakeOverrides.kt
index cd5cf15f938..ede7907a138 100644
--- a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/FakeOverrides.kt
+++ b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/FakeOverrides.kt
@@ -23,6 +23,7 @@ import org.jetbrains.kotlin.ir.descriptors.WrappedPropertyDescriptor
 import org.jetbrains.kotlin.ir.descriptors.WrappedSimpleFunctionDescriptor
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.symbols.IrSymbol
+import org.jetbrains.kotlin.ir.symbols.IrTypeParameterSymbol
 import org.jetbrains.kotlin.ir.symbols.impl.IrPropertySymbolImpl
 import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.types.IrType
@@ -68,22 +69,24 @@ class FakeOverrideBuilder(
         val classifier = superType.classifier
         require(classifier is IrClassSymbol) { "superType classifier is not IrClassSymbol: $classifier" }
 
-        val typeParameters = extractTypeParameters(classifier.owner).map { it.symbol }
-        val typeArguments = superType.arguments.map {
-            require(it is IrTypeProjection) { "Unexpected super type argument: $it" }
-            assert(it.variance == Variance.INVARIANT) { "Unexpected variance in super type argument: ${it.variance}" }
-            it.type
+        val typeParameters = extractTypeParameters(classifier.owner)
+        val superArguments = superType.arguments
+        assert(typeParameters.size == superArguments.size) {
+            "typeParameters = $typeParameters size != typeArguments = $superArguments size "
         }
 
-        assert(typeParameters.size == typeArguments.size) {
-            "typeParameters = $typeParameters size != typeArguments = $typeArguments size "
+        val substitutionMap = mutableMapOf<IrTypeParameterSymbol, IrType>()
+
+        for (i in typeParameters.indices) {
+            val tp = typeParameters[i]
+            val ta = superArguments[i]
+            require(ta is IrTypeProjection) { "Unexpected super type argument: $ta @ $i" }
+            assert(ta.variance == Variance.INVARIANT) { "Unexpected variance in super type argument: ${ta.variance} @$i" }
+            substitutionMap[tp.symbol] = ta.type
         }
 
-        val substitutionMap = typeParameters.zip(typeArguments).toMap()
-        val copier =
-            DeepCopyIrTreeWithSymbolsForFakeOverrides(substitutionMap, superType, clazz)
-
-        val deepCopyFakeOverride = copier.copy(member) as IrOverridableMember
+        val copier = DeepCopyIrTreeWithSymbolsForFakeOverrides(substitutionMap)
+        val deepCopyFakeOverride = copier.copy(member, clazz) as IrOverridableMember
         deepCopyFakeOverride.parent = clazz
 
         return deepCopyFakeOverride
diff --git a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/IrOverridingUtil.kt b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/IrOverridingUtil.kt
index e163ee4561f..6ddce727b01 100644
--- a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/IrOverridingUtil.kt
+++ b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/IrOverridingUtil.kt
@@ -100,18 +100,16 @@ class IrOverridingUtil(
     fun buildFakeOverridesForClass(clazz: IrClass) {
         val superTypes = allPublicApiSuperTypesOrAny(clazz)
 
-        val fromCurrent = clazz.declarations
-            .filterIsInstance<IrOverridableMember>()
-            .filter { it.symbol.isPublicApi }
+        val fromCurrent = clazz.declarations.filter { it is IrOverridableMember && it.symbol.isPublicApi } as List<IrOverridableMember>
 
         val allFromSuper = superTypes.flatMap { superType ->
             val superClass = superType.getClass() ?: error("Unexpected super type: $superType")
             superClass.declarations
-                .filterIsInstance<IrOverridableMember>()
-                .filter { it.symbol.isPublicApi }
+                .filter { it is IrOverridableMember && it.symbol.isPublicApi }
                 .map {
-                    val fakeOverride = fakeOverrideBuilder.fakeOverrideMember(superType, it, clazz)
-                    originals[fakeOverride] = it
+                    val overridenMember = it as IrOverridableMember
+                    val fakeOverride = fakeOverrideBuilder.fakeOverrideMember(superType, overridenMember, clazz)
+                    originals[fakeOverride] = overridenMember
                     originalSuperTypes[fakeOverride] = superType
                     fakeOverride
                 }