diff --git a/libraries/tools/kotlin-maven-serialization/pom.xml b/libraries/tools/kotlin-maven-serialization/pom.xml
index 4dc8161e81f..a3bbcc61ed8 100755
--- a/libraries/tools/kotlin-maven-serialization/pom.xml
+++ b/libraries/tools/kotlin-maven-serialization/pom.xml
@@ -17,7 +17,7 @@
     <groupId>org.jetbrains.kotlinx</groupId>
     <artifactId>kotlinx-maven-serialization-plugin</artifactId>
     <packaging>jar</packaging>
-    <version>0.1</version>
+    <version>0.1.1</version>
 
     <description>Serialization plugin for Maven</description>
 
diff --git a/libraries/tools/kotlin-serialization/build.gradle b/libraries/tools/kotlin-serialization/build.gradle
index 62056d168a5..bcb8b3fbaf6 100644
--- a/libraries/tools/kotlin-serialization/build.gradle
+++ b/libraries/tools/kotlin-serialization/build.gradle
@@ -3,7 +3,7 @@ plugins {
 }
 
 group = 'org.jetbrains.kotlinx'
-version = '0.1'
+version = '0.1.1'
 
 apply plugin: 'kotlin'
 
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializerCodegen.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializerCodegen.kt
index 2d85f0c6314..33e7d557212 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializerCodegen.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializerCodegen.kt
@@ -80,13 +80,13 @@ abstract class SerializerCodegen(declaration: KtPureClassOrObject, bindingContex
     fun getPropertyToGenerate(
             classDescriptor: ClassDescriptor,
             name: String,
-            isReturnTypeOk: (KotlinType) -> Boolean
+            isReturnTypeOk: (PropertyDescriptor) -> Boolean
     ): PropertyDescriptor? =
             classDescriptor.unsubstitutedMemberScope.getContributedVariables(Name.identifier(name), NoLookupLocation.FROM_BACKEND)
                     .singleOrNull { property ->
                         property.kind.let { kind -> kind == CallableMemberDescriptor.Kind.SYNTHESIZED || kind == CallableMemberDescriptor.Kind.FAKE_OVERRIDE } &&
                         property.modality != Modality.FINAL &&
                         property.returnType != null &&
-                        isReturnTypeOk(property.returnType!!)
+                        isReturnTypeOk(property)
                     }
 }
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/js/SerializerJsTranslator.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/js/SerializerJsTranslator.kt
index 01ba9362d15..98385cc2370 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/js/SerializerJsTranslator.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/js/SerializerJsTranslator.kt
@@ -272,20 +272,20 @@ class SerializerJsTranslator(declaration: KtPureClassOrObject,
                                            bitMasks[i / 32],
                                            JsIntLiteral(bitPos)
                         ).makeStmt()
-                        // if (!readAll) break -- but only if this is last prop
-                        if (i != orderedProperties.lastIndex)
-                            +JsIf(JsAstUtils.not(readAllVar), JsBreak())
-                        else {
-                            // if (readAll) breakLoop else break
-                            +JsIf(readAllVar, JsBreak(loopRef), JsBreak())
-                        }
+                        // if (!readAll) break
+                        +JsIf(JsAstUtils.not(readAllVar), JsBreak())
                     }
                 }
-                // case -1, default: break loop
-                case(JsIntLiteral(-1)) {}
-                default {
+                // case -1: break loop
+                case(JsIntLiteral(-1)) {
                     +JsBreak(loopRef)
                 }
+                // default: throw
+                default {
+                    val excClassRef = serializableDescriptor.getClassFromSerializationPackage("UnknownFieldException")
+                            .let { context.getQualifiedReference(it) }
+                    +JsThrow(JsNew(excClassRef, listOf(indexVar)))
+                }
             }
         }, loop)
 
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/JVMCodegenUtil.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/JVMCodegenUtil.kt
index 49fa38c9d80..338432f00c9 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/JVMCodegenUtil.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/JVMCodegenUtil.kt
@@ -51,6 +51,7 @@ internal val kSerializerArrayType = Type.getObjectType("[Lkotlinx/serialization/
 
 internal val serializationExceptionName = "kotlinx/serialization/SerializationException"
 internal val serializationExceptionMissingFieldName = "kotlinx/serialization/MissingFieldException"
+internal val serializationExceptionUnknownIndexName = "kotlinx/serialization/UnknownFieldException"
 
 val OPT_MASK_TYPE: Type = Type.INT_TYPE
 val OPT_MASK_BITS = 32
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 45d861a3bd0..d863e95562f 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
@@ -24,6 +24,7 @@ import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.descriptors.PropertyDescriptor
 import org.jetbrains.kotlin.psi.KtParameter
+import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.descriptorUtil.getSuperClassOrAny
 import org.jetbrains.kotlin.resolve.jvm.jvmSignature.JvmMethodSignature
 import org.jetbrains.kotlinx.serialization.compiler.backend.common.SerializableCodegen
@@ -140,6 +141,8 @@ class SerializableCodegenImpl(
                 goTo(nextLabel)
                 visitLabel(setLbl)
                 // setting defaultValue
+                if (classCodegen.bindingContext[BindingContext.BACKING_FIELD_REQUIRED, prop.descriptor] != true)
+                    throw CompilationException("Optional properties without backing fields doesn't have much sense, maybe you want transient?", null, getProp(prop))
                 exprCodegen.genInitProperty(prop)
                 visitLabel(nextLabel)
             }
@@ -150,6 +153,7 @@ class SerializableCodegenImpl(
         val serializedProps = properties.serializableProperties.map { it.descriptor }
 
         (descToProps - serializedProps)
+                .filter { classCodegen.shouldInitializeProperty(it.value) }
                 .forEach { (_, prop) -> classCodegen.initializeProperty(exprCodegen, prop) }
         (paramsToProps - serializedProps)
                 .forEach { (t, u) -> exprCodegen.genInitParam(t, u) }
@@ -168,7 +172,8 @@ class SerializableCodegenImpl(
         load(0, thisAsmType)
 
         if (!superClass.isInternalSerializable) {
-            require(superClass.constructors.firstOrNull { it.valueParameters.isEmpty() } != null) { "Non-serializable parent of serializable class must have no arg constructor" }
+            require(superClass.constructors.firstOrNull { it.valueParameters.isEmpty() } != null,
+                    { "Non-serializable parent of serializable $serializableDescriptor must have no arg constructor" })
 
             // call
             invokespecial(superType, "<init>", "()V", false)
@@ -191,14 +196,18 @@ class SerializableCodegenImpl(
     }
               ?: getParam(prop)?.let {
         this.v.load(0, thisAsmType)
+        if (!it.hasDefaultValue()) throw CompilationException("Optional field ${it.name} in primary constructor of serializable " +
+                                                                 "$serializableDescriptor must have default value", null, it)
         this.gen(it.defaultValue, prop.asmType)
-        this.v.putfield(thisAsmType.internalName, prop.name, prop.asmType.descriptor)
+        this.v.putfield(thisAsmType.internalName, prop.descriptor.name.asString(), prop.asmType.descriptor)
     }
               ?: throw IllegalStateException()
 
     private fun ExpressionCodegen.genInitParam(prop: PropertyDescriptor, param: KtParameter) {
         this.v.load(0, thisAsmType)
         val mapType = classCodegen.typeMapper.mapType(prop.type)
+        if (!param.hasDefaultValue()) throw CompilationException("Transient field ${param.name} in primary constructor of serializable " +
+                                                                 "$serializableDescriptor must have default value", null, param)
         this.gen(param.defaultValue, mapType)
         this.v.putfield(thisAsmType.internalName, prop.name.asString(), mapType.descriptor)
     }
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializerCodegenImpl.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializerCodegenImpl.kt
index b09058942d8..82cc23630ac 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializerCodegenImpl.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializerCodegenImpl.kt
@@ -210,6 +210,7 @@ class SerializerCodegenImpl(
             val labeledProperties = orderedProperties.filter { !it.transient }
             val readAllLabel = Label()
             val readEndLabel = Label()
+            val incorrectIndLabel = Label()
             val labels = arrayOfNulls<Label>(labeledProperties.size + 2)
             labels[0] = readAllLabel // READ_ALL
             labels[1] = readEndLabel // READ_DONE
@@ -217,8 +218,7 @@ class SerializerCodegenImpl(
                 labels[i + 2] = Label()
             }
             load(indexVar, Type.INT_TYPE)
-            // todo: readEnd is currently default, should probably throw exception instead
-            tableswitch(-2, labeledProperties.size - 1, readEndLabel, *labels)
+            tableswitch(-2, labeledProperties.size - 1, incorrectIndLabel, *labels)
             // readAll: readAll := true
             visitLabel(readAllLabel)
             iconst(1)
@@ -315,6 +315,15 @@ class SerializerCodegenImpl(
             }
             // return
             areturn(serializableAsmType)
+
+            // throwing an exception in default branch (if no index matched)
+            visitLabel(incorrectIndLabel)
+            anew(Type.getObjectType(serializationExceptionUnknownIndexName))
+            dup()
+            load(indexVar, Type.INT_TYPE)
+            invokespecial(serializationExceptionUnknownIndexName, "<init>", "(I)V", false)
+            checkcast(Type.getObjectType("java/lang/Throwable"))
+            athrow()
         }
     }
 
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 0a53f641ecf..c50e5bdb747 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
@@ -27,6 +27,7 @@ import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.descriptorUtil.module
 import org.jetbrains.kotlin.types.*
+import org.jetbrains.kotlin.types.typeUtil.isSubtypeOf
 
 internal val packageFqName = FqName("kotlinx.serialization")
 internal val internalPackageFqName = FqName("kotlinx.serialization.internal")
@@ -147,8 +148,8 @@ fun getSerializableClassDescriptorBySerializer(serializerDescriptor: ClassDescri
     return classDescriptor
 }
 
-// todo: serialization: do an actual check
-fun ClassDescriptor.checkSerializableClassPropertyResult(type: KotlinType): Boolean = true
+fun ClassDescriptor.checkSerializableClassPropertyResult(prop: PropertyDescriptor): Boolean =
+        prop.returnType!!.isSubtypeOf(getClassFromSerializationPackage("KSerialClassDesc").toSimpleType(false)) // todo: cache lookup
 
 // todo: serialization: do an actual check better that just number of parameters
 fun ClassDescriptor.checkSaveMethodParameters(parameters: List<ValueParameterDescriptor>): Boolean =
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializerDescriptorResolver.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializerDescriptorResolver.kt
index 1c80daa7829..e5da709df37 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializerDescriptorResolver.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializerDescriptorResolver.kt
@@ -94,10 +94,10 @@ object KSerializerDescriptorResolver {
                                      fromSupertypes: ArrayList<PropertyDescriptor>,
                                      name: Name,
                                      result: MutableSet<PropertyDescriptor>) {
-        val classDescriptor = getSerializableClassDescriptorBySerializer(thisDescriptor) ?: return
-        // todo: check if it is already defined
-        if (name == SERIAL_DESC_FIELD_NAME)
-            result.add(createSerializableClassPropertyDescriptor(thisDescriptor, classDescriptor))
+       val classDescriptor = getSerializableClassDescriptorBySerializer(thisDescriptor) ?: return
+        if (name == SERIAL_DESC_FIELD_NAME && result.none(thisDescriptor::checkSerializableClassPropertyResult) &&
+            fromSupertypes.none { thisDescriptor.checkSerializableClassPropertyResult(it) && it.modality == Modality.FINAL} )
+                result.add(createSerializableClassPropertyDescriptor(thisDescriptor, classDescriptor))
 
     }