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 f6f77a32bb3..d6334ea2ccb 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
@@ -23,7 +23,7 @@ import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlinx.serialization.compiler.resolve.KSerializerDescriptorResolver
 import org.jetbrains.kotlinx.serialization.compiler.resolve.SerializableProperties
 import org.jetbrains.kotlinx.serialization.compiler.resolve.classSerializer
-import org.jetbrains.kotlinx.serialization.compiler.resolve.toClassDescriptor
+import org.jetbrains.kotlinx.serialization.compiler.resolve.isAbstractSerializableClass
 
 abstract class SerializableCodegen(
     protected val serializableDescriptor: ClassDescriptor,
@@ -37,16 +37,16 @@ abstract class SerializableCodegen(
     }
 
     private fun generateSyntheticInternalConstructor() {
-        val serializerDescriptor = serializableDescriptor.classSerializer?.toClassDescriptor ?: return
-        if (SerializerCodegen.getSyntheticLoadMember(serializerDescriptor) != null) {
+        val serializerDescriptor = serializableDescriptor.classSerializer ?: return
+        if (isAbstractSerializableClass(serializableDescriptor) || SerializerCodegen.getSyntheticLoadMember(serializerDescriptor) != null) {
             val constrDesc = KSerializerDescriptorResolver.createLoadConstructorDescriptor(serializableDescriptor, bindingContext)
             generateInternalConstructor(constrDesc)
         }
     }
 
     private fun generateSyntheticMethods() {
-        val serializerDescriptor = serializableDescriptor.classSerializer?.toClassDescriptor ?: return
-        if (SerializerCodegen.getSyntheticSaveMember(serializerDescriptor) != null) {
+        val serializerDescriptor = serializableDescriptor.classSerializer ?: return
+        if (isAbstractSerializableClass(serializableDescriptor) || SerializerCodegen.getSyntheticSaveMember(serializerDescriptor) != null) {
             val func = KSerializerDescriptorResolver.createWriteSelfFunctionDescriptor(serializableDescriptor)
             generateWriteSelfMethod(func)
         }
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/TypeUtil.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/TypeUtil.kt
index 81627387ddd..868f8721e0c 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/TypeUtil.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/TypeUtil.kt
@@ -30,11 +30,9 @@ import org.jetbrains.kotlin.psi.KtParameter
 import org.jetbrains.kotlin.psi.KtProperty
 import org.jetbrains.kotlin.psi.KtPureClassOrObject
 import org.jetbrains.kotlin.resolve.BindingContext
-import org.jetbrains.kotlin.resolve.descriptorUtil.getSuperClassNotAny
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.typeUtil.*
 import org.jetbrains.kotlinx.serialization.compiler.backend.jvm.enumSerializerId
-import org.jetbrains.kotlinx.serialization.compiler.backend.jvm.polymorphicSerializerId
 import org.jetbrains.kotlinx.serialization.compiler.backend.jvm.referenceArraySerializerId
 import org.jetbrains.kotlinx.serialization.compiler.resolve.*
 import org.jetbrains.kotlinx.serialization.compiler.resolve.SerializationPackages.internalPackageFqName
@@ -130,9 +128,11 @@ fun findTypeSerializer(module: ModuleDescriptor, kType: KotlinType): ClassDescri
     if (userOverride != null) return userOverride.toClassDescriptor
     if (kType.isTypeParameter()) return null
     if (KotlinBuiltIns.isArray(kType)) return module.getClassFromInternalSerializationPackage(SpecialBuiltins.referenceArraySerializer)
-    return kType.typeSerializer.toClassDescriptor // check for serializer defined on the type
-            ?: findStandardKotlinTypeSerializer(module, kType) // otherwise see if there is a standard serializer
-            ?: findEnumTypeSerializer(module, kType)
+    val stdSer = findStandardKotlinTypeSerializer(module, kType) // see if there is a standard serializer
+        ?: findEnumTypeSerializer(module, kType)
+    if (stdSer != null) return stdSer
+    if (kType.isInterface()) return module.getClassFromSerializationPackage(SpecialBuiltins.polymorphicSerializer)
+    return kType.toClassDescriptor?.classSerializer // check for serializer defined on the type
 }
 
 fun findStandardKotlinTypeSerializer(module: ModuleDescriptor, kType: KotlinType): ClassDescriptor? {
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableCompanionIrGenerator.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableCompanionIrGenerator.kt
index f32e776b3e8..6894dddc89c 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableCompanionIrGenerator.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableCompanionIrGenerator.kt
@@ -12,7 +12,10 @@ import org.jetbrains.kotlin.ir.util.TypeTranslator
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.descriptorUtil.module
 import org.jetbrains.kotlinx.serialization.compiler.backend.common.SerializableCompanionCodegen
-import org.jetbrains.kotlinx.serialization.compiler.resolve.*
+import org.jetbrains.kotlinx.serialization.compiler.resolve.KSerializerDescriptorResolver
+import org.jetbrains.kotlinx.serialization.compiler.resolve.classSerializer
+import org.jetbrains.kotlinx.serialization.compiler.resolve.getSerializableClassDescriptorByCompanion
+import org.jetbrains.kotlinx.serialization.compiler.resolve.shouldHaveGeneratedMethodsInCompanion
 
 class SerializableCompanionIrGenerator(
     val irClass: IrClass,
@@ -39,7 +42,7 @@ class SerializableCompanionIrGenerator(
 
     override fun generateSerializerGetter(methodDescriptor: FunctionDescriptor) =
         irClass.contributeFunction(methodDescriptor, fromStubs = true) { getter ->
-            val serializer = serializableDescriptor.classSerializer?.toClassDescriptor!!
+            val serializer = serializableDescriptor.classSerializer!!
             val expr = if (serializer.kind == ClassKind.OBJECT) {
                 irGetObject(serializer)
             } else {
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/js/SerializableCompanionJsTranslator.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/js/SerializableCompanionJsTranslator.kt
index 692431b7035..04ff8d86a3f 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/js/SerializableCompanionJsTranslator.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/js/SerializableCompanionJsTranslator.kt
@@ -27,7 +27,10 @@ import org.jetbrains.kotlin.js.translate.context.TranslationContext
 import org.jetbrains.kotlin.js.translate.declaration.DeclarationBodyVisitor
 import org.jetbrains.kotlin.psi.KtPureClassOrObject
 import org.jetbrains.kotlinx.serialization.compiler.backend.common.SerializableCompanionCodegen
-import org.jetbrains.kotlinx.serialization.compiler.resolve.*
+import org.jetbrains.kotlinx.serialization.compiler.resolve.KSerializerDescriptorResolver
+import org.jetbrains.kotlinx.serialization.compiler.resolve.classSerializer
+import org.jetbrains.kotlinx.serialization.compiler.resolve.getSerializableClassDescriptorByCompanion
+import org.jetbrains.kotlinx.serialization.compiler.resolve.shouldHaveGeneratedMethodsInCompanion
 
 class SerializableCompanionJsTranslator(
     declaration: ClassDescriptor,
@@ -37,7 +40,7 @@ class SerializableCompanionJsTranslator(
 
     override fun generateSerializerGetter(methodDescriptor: FunctionDescriptor) {
         val f = context.buildFunction(methodDescriptor) {jsFun, context ->
-            val serializer = serializableDescriptor.classSerializer?.toClassDescriptor!!
+            val serializer = serializableDescriptor.classSerializer!!
             val stmt: JsExpression = if (serializer.kind == ClassKind.OBJECT) {
                 context.serializerObjectGetter(serializer)
             } else {
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializableCompanionCodegenImpl.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializableCompanionCodegenImpl.kt
index ab73ff9bdfc..ae7a1018854 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializableCompanionCodegenImpl.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializableCompanionCodegenImpl.kt
@@ -20,7 +20,9 @@ import org.jetbrains.kotlin.codegen.ImplementationBodyCodegen
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.resolve.descriptorUtil.module
 import org.jetbrains.kotlinx.serialization.compiler.backend.common.SerializableCompanionCodegen
-import org.jetbrains.kotlinx.serialization.compiler.resolve.*
+import org.jetbrains.kotlinx.serialization.compiler.resolve.classSerializer
+import org.jetbrains.kotlinx.serialization.compiler.resolve.getSerializableClassDescriptorByCompanion
+import org.jetbrains.kotlinx.serialization.compiler.resolve.shouldHaveGeneratedMethodsInCompanion
 
 class SerializableCompanionCodegenImpl(private val classCodegen: ImplementationBodyCodegen) :
     SerializableCompanionCodegen(classCodegen.descriptor, classCodegen.bindingContext) {
@@ -34,7 +36,7 @@ class SerializableCompanionCodegenImpl(private val classCodegen: ImplementationB
     }
 
     override fun generateSerializerGetter(methodDescriptor: FunctionDescriptor) {
-        val serial = serializableDescriptor.classSerializer?.toClassDescriptor ?: return
+        val serial = serializableDescriptor.classSerializer ?: return
         classCodegen.generateMethod(methodDescriptor) { _, _ ->
             stackValueSerializerInstance(
                 classCodegen,
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 1800942a742..4c0c9f24713 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
@@ -117,19 +117,33 @@ internal val ClassDescriptor.hasSerializableAnnotationWithoutArgs: Boolean
         return psi.valueArguments.isEmpty()
     }
 
+// For abstract classes marked with @Serializable,
+// methods are generated anyway although they shouldn't have
+// generated $serializer and use Polymorphic one.
+internal fun isAbstractSerializableClass(serializableDescriptor: ClassDescriptor): Boolean =
+    serializableDescriptor.isInternalSerializable && serializableDescriptor.modality == Modality.ABSTRACT
+
+internal fun ClassDescriptor.polymorphicSerializerIfApplicableAutomatically(): ClassDescriptor? = if (
+    isAbstractSerializableClass(this)
+    || kind == ClassKind.INTERFACE
+) module.getClassFromSerializationPackage(SpecialBuiltins.polymorphicSerializer)
+else null
+
 // serializer that was declared for this type
-internal val ClassDescriptor?.classSerializer: KotlinType?
+internal val ClassDescriptor?.classSerializer: ClassDescriptor?
     get() = this?.let {
         // serializer annotation on class?
-        serializableWith?.let { return it }
+        serializableWith?.let { return it.toClassDescriptor }
         // companion object serializer?
-        if (hasCompanionObjectAsSerializer) return companionObjectDescriptor?.defaultType
+        if (hasCompanionObjectAsSerializer) return companionObjectDescriptor
+        // can infer @Poly?
+        polymorphicSerializerIfApplicableAutomatically()?.let { return it }
         // default serializable?
         if (isInternalSerializable) {
             // $serializer nested class
             return this.unsubstitutedMemberScope
-                    .getDescriptorsFiltered(nameFilter = {it == SerialEntityNames.SERIALIZER_CLASS_NAME})
-                    .filterIsInstance<ClassDescriptor>().singleOrNull()?.defaultType
+                .getDescriptorsFiltered(nameFilter = { it == SerialEntityNames.SERIALIZER_CLASS_NAME })
+                .filterIsInstance<ClassDescriptor>().singleOrNull()
         }
         return null
     }
@@ -139,8 +153,8 @@ internal val ClassDescriptor.hasCompanionObjectAsSerializer: Boolean
 
 internal fun checkSerializerNullability(classType: KotlinType, serializerType: KotlinType): KotlinType {
     val castedToKSerial = requireNotNull(
-            serializerType.supertypes().find { isKSerializer(it) },
-            { "${KSERIALIZER_CLASS} is not a supertype of $serializerType" }
+        serializerType.supertypes().find { isKSerializer(it) },
+        { "${KSERIALIZER_CLASS} is not a supertype of $serializerType" }
     )
     if (!classType.isMarkedNullable && castedToKSerial.arguments.first().type.isMarkedNullable)
         throw IllegalStateException("Can't serialize non-nullable field of type ${classType} with nullable serializer ${serializerType}")
@@ -149,11 +163,13 @@ internal fun checkSerializerNullability(classType: KotlinType, serializerType: K
 
 // returns only user-overriden Serializer
 val KotlinType.overridenSerializer: KotlinType?
-    get() = (this.toClassDescriptor?.serializableWith)?.let { checkSerializerNullability(this, it) }
-
-// serializer that was declared for this specific type or annotation from a class declaration
-val KotlinType.typeSerializer: KotlinType?
-    get() = this.toClassDescriptor?.classSerializer
+    get() {
+        val desc = this.toClassDescriptor ?: return null
+        (desc.serializableWith)?.let { return checkSerializerNullability(this, it) }
+        if (desc.annotations.hasAnnotation(SerializationAnnotations.polymorphicFqName))
+            return desc.module.getClassFromSerializationPackage(SpecialBuiltins.polymorphicSerializer).defaultType
+        return null
+    }
 
 val KotlinType.genericIndex: Int?
     get() = (this.constructor.declarationDescriptor as? TypeParameterDescriptor)?.index