diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializableCodegen.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializableCodegen.kt
index 7093fd314e2cc..a6344f077e237 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializableCodegen.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializableCodegen.kt
@@ -26,7 +26,7 @@ abstract class SerializableCodegen(
     }
 
     private inline fun ClassDescriptor.shouldHaveSpecificSyntheticMethods(functionPresenceChecker: () -> FunctionDescriptor?) =
-        !isInlineClass() && (isAbstractSerializableClass() || isSealedSerializableClass() || functionPresenceChecker() != null)
+        !isInlineClass() && (isAbstractOrSealedSerializableClass() || functionPresenceChecker() != null)
 
     private fun generateSyntheticInternalConstructor() {
         val serializerDescriptor = serializableDescriptor.classSerializer ?: return
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializableCompanionCodegen.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializableCompanionCodegen.kt
index 7684a1d19f558..7ca9f081d49d4 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializableCompanionCodegen.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializableCompanionCodegen.kt
@@ -1,17 +1,6 @@
 /*
- * Copyright 2010-2017 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlinx.serialization.compiler.backend.common
@@ -44,7 +33,7 @@ abstract class SerializableCompanionCodegen(
                     "probably clash with user-defined function has occurred"
         )
 
-        if (serializableDescriptor.isSerializableObject || serializableDescriptor.isSealedSerializableClass() || serializableDescriptor.isAbstractSerializableClass()) {
+        if (serializableDescriptor.isSerializableObject || serializableDescriptor.isAbstractOrSealedSerializableClass()) {
             generateLazySerializerGetter(serializerGetterDescriptor)
         } else {
             generateSerializerGetter(serializerGetterDescriptor)
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableIrGenerator.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableIrGenerator.kt
index 123d26a04c37d..4ecb4ca49c106 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableIrGenerator.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableIrGenerator.kt
@@ -110,7 +110,7 @@ class SerializableIrGenerator(
 
             if (useFieldMissingOptimization() &&
                 // for abstract classes fields MUST BE checked in child classes
-                !serializableDescriptor.isAbstractSerializableClass() && !serializableDescriptor.isSealedSerializableClass()
+                !serializableDescriptor.isAbstractOrSealedSerializableClass()
             ) {
                 val getDescriptorExpr = if (serializableDescriptor.isStaticSerializable) {
                     getStaticSerialDescriptorExpr()
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializableCodegenImpl.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializableCodegenImpl.kt
index 4d7baeb972350..f22f03bbe145b 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializableCodegenImpl.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializableCodegenImpl.kt
@@ -1,17 +1,6 @@
 /*
- * Copyright 2010-2021 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlinx.serialization.compiler.backend.jvm
@@ -285,7 +274,7 @@ class SerializableCodegenImpl(
     }
 
     private fun InstructionAdapter.generateOptimizedGoldenMaskCheck(maskVar: Int) {
-        if (serializableDescriptor.isAbstractSerializableClass() || serializableDescriptor.isSealedSerializableClass()) {
+        if (serializableDescriptor.isAbstractOrSealedSerializableClass()) {
             // for abstract classes fields MUST BE checked in child classes
             return
         }
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializationUtil.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializationUtil.kt
index 6422842b287f0..546af42355bf3 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializationUtil.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializationUtil.kt
@@ -1,17 +1,6 @@
 /*
- * Copyright 2010-2017 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlinx.serialization.compiler.resolve
@@ -156,17 +145,14 @@ internal fun Annotated.findSerializableAnnotationDeclaration(): KtAnnotationEntr
 // For abstract classes marked with @Serializable,
 // methods are generated anyway although they shouldn't have
 // generated $serializer and use Polymorphic one.
-internal fun ClassDescriptor.isAbstractSerializableClass(): Boolean =
-    isInternalSerializable && modality == Modality.ABSTRACT
-
-internal fun ClassDescriptor.isSealedSerializableClass(): Boolean =
-    isInternalSerializable && modality == Modality.SEALED
+internal fun ClassDescriptor.isAbstractOrSealedSerializableClass(): Boolean =
+    isInternalSerializable && (modality == Modality.ABSTRACT || modality == Modality.SEALED)
 
 internal fun ClassDescriptor.polymorphicSerializerIfApplicableAutomatically(): ClassDescriptor? {
     val serializer = when {
-        this.isAbstractSerializableClass()
-                || kind == ClassKind.INTERFACE -> SpecialBuiltins.polymorphicSerializer
-        this.isSealedSerializableClass() -> SpecialBuiltins.sealedSerializer
+        kind == ClassKind.INTERFACE -> SpecialBuiltins.polymorphicSerializer
+        isInternalSerializable && modality == Modality.ABSTRACT -> SpecialBuiltins.polymorphicSerializer
+        isInternalSerializable && modality == Modality.SEALED -> SpecialBuiltins.sealedSerializer
         else -> null
     }
     return serializer?.let { module.getClassFromSerializationPackage(it) }
@@ -217,6 +203,7 @@ internal fun ClassDescriptor.needSerializerFactory(): Boolean {
     if (!(this.platform?.isNative() == true || this.platform.isJs())) return false
     val serializableClass = getSerializableClassDescriptorByCompanion(this) ?: return false
     if (serializableClass.isSerializableObject) return true
+    if (serializableClass.isAbstractOrSealedSerializableClass()) return true
     if (serializableClass.declaredTypeParameters.isEmpty()) return false
     return true
 }