diff --git a/build.xml b/build.xml
index 0a8c4c4b5f7..e3a043da7ea 100644
--- a/build.xml
+++ b/build.xml
@@ -423,6 +423,14 @@
             <arg value="core/builtins/native"/>
             <arg value="core/builtins/src"/>
         </java>
+
+        <!-- TODO: remove after bootstrap -->
+        <copy file="${output}/builtins/kotlin/.kotlin_package" tofile="${output}/builtins/kotlin/kotlin.kotlin_package"/>
+        <copy file="${output}/builtins/kotlin/.kotlin_string_table" tofile="${output}/builtins/kotlin/kotlin.kotlin_string_table"/>
+        <copy file="${output}/builtins/kotlin/internal/.kotlin_package" tofile="${output}/builtins/kotlin/internal/internal.kotlin_package"/>
+        <copy file="${output}/builtins/kotlin/internal/.kotlin_string_table" tofile="${output}/builtins/kotlin/internal/internal.kotlin_string_table"/>
+        <copy file="${output}/builtins/kotlin/reflect/.kotlin_package" tofile="${output}/builtins/kotlin/reflect/reflect.kotlin_package"/>
+        <copy file="${output}/builtins/kotlin/reflect/.kotlin_string_table" tofile="${output}/builtins/kotlin/reflect/reflect.kotlin_string_table"/>
     </target>
 
     <macrodef name="pack-compiler">
diff --git a/compiler/builtins-serializer/src/org/jetbrains/kotlin/serialization/builtins/BuiltInsSerializer.kt b/compiler/builtins-serializer/src/org/jetbrains/kotlin/serialization/builtins/BuiltInsSerializer.kt
index 5e28b5c9973..2154266688c 100644
--- a/compiler/builtins-serializer/src/org/jetbrains/kotlin/serialization/builtins/BuiltInsSerializer.kt
+++ b/compiler/builtins-serializer/src/org/jetbrains/kotlin/serialization/builtins/BuiltInsSerializer.kt
@@ -128,20 +128,25 @@ public class BuiltInsSerializer(private val dependOnOldBuiltIns: Boolean) {
         val fragments = module.getPackageFragmentProvider().getPackageFragments(fqName)
         val packageProto = serializer.packageProto(fragments).build() ?: error("Package fragments not serialized: $fragments")
         packageProto.writeTo(packageStream)
-        write(destDir, BuiltInsSerializationUtil.getPackageFilePath(fqName), packageStream)
+        write(destDir, BuiltInsSerializationUtil.getPackageFilePath(fqName), packageStream,
+              BuiltInsSerializationUtil.FallbackPaths.getPackageFilePath(fqName))
 
         val nameStream = ByteArrayOutputStream()
         val strings = serializer.getStringTable()
         SerializationUtil.serializeStringTable(nameStream, strings.serializeSimpleNames(), strings.serializeQualifiedNames())
-        write(destDir, BuiltInsSerializationUtil.getStringTableFilePath(fqName), nameStream)
+        write(destDir, BuiltInsSerializationUtil.getStringTableFilePath(fqName), nameStream,
+              BuiltInsSerializationUtil.FallbackPaths.getStringTableFilePath(fqName))
     }
 
-    private fun write(destDir: File, fileName: String, stream: ByteArrayOutputStream) {
+    internal /* KT-5786 */ fun write(destDir: File, fileName: String, stream: ByteArrayOutputStream, legacyFileName: String? = null) {
         totalSize += stream.size()
         totalFiles++
-        val file = File(destDir, fileName)
-        file.getParentFile()?.mkdirs()
-        file.writeBytes(stream.toByteArray())
+        File(destDir, fileName).getParentFile().mkdirs()
+        File(destDir, fileName).writeBytes(stream.toByteArray())
+
+        legacyFileName?.let { fileName ->
+            File(destDir, fileName).writeBytes(stream.toByteArray())
+        }
     }
 
     private fun serializeClass(
diff --git a/compiler/builtins-serializer/src/org/jetbrains/kotlin/serialization/builtins/run.kt b/compiler/builtins-serializer/src/org/jetbrains/kotlin/serialization/builtins/run.kt
index f5804bebc2c..30ef62bad92 100644
--- a/compiler/builtins-serializer/src/org/jetbrains/kotlin/serialization/builtins/run.kt
+++ b/compiler/builtins-serializer/src/org/jetbrains/kotlin/serialization/builtins/run.kt
@@ -29,7 +29,7 @@ Usage: ... <destination dir> (<source dir>)+
 
 Analyzes Kotlin sources found in the given source directories and serializes
 found top-level declarations to <destination dir> (files such as
-.kotlin_string_table, .kotlin_package, *.kotlin_class)"""
+*.kotlin_string_table, *.kotlin_package, *.kotlin_class)"""
         )
         return
     }
diff --git a/core/descriptors/src/org/jetbrains/kotlin/builtins/BuiltInsSerializationUtil.kt b/core/descriptors/src/org/jetbrains/kotlin/builtins/BuiltInsSerializationUtil.kt
index a3480c4e747..a709eb7d4c0 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/builtins/BuiltInsSerializationUtil.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/builtins/BuiltInsSerializationUtil.kt
@@ -20,7 +20,6 @@ import com.google.protobuf.ExtensionRegistryLite
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.serialization.builtins.BuiltInsProtoBuf
-import kotlin.platform.platformStatic
 
 public object BuiltInsSerializationUtil {
     public val EXTENSION_REGISTRY: ExtensionRegistryLite
@@ -31,20 +30,33 @@ public object BuiltInsSerializationUtil {
     }
 
     private val CLASS_METADATA_FILE_EXTENSION = "kotlin_class"
-    private val PACKAGE_FILE_NAME = ".kotlin_package"
-    private val STRING_TABLE_FILE_NAME = ".kotlin_string_table"
+    private val PACKAGE_FILE_EXTENSION = "kotlin_package"
+    private val STRING_TABLE_FILE_EXTENSION = "kotlin_string_table"
 
-    platformStatic public fun getClassMetadataPath(classId: ClassId): String {
+    // TODO: remove this after M12
+    public object FallbackPaths {
+        public fun getPackageFilePath(fqName: FqName): String =
+                packageFqNameToPath(fqName) + "/.kotlin_package"
+
+        public fun getStringTableFilePath(fqName: FqName): String =
+                packageFqNameToPath(fqName) + "/.kotlin_string_table"
+    }
+
+    public fun getClassMetadataPath(classId: ClassId): String {
         return packageFqNameToPath(classId.getPackageFqName()) + "/" + classId.getRelativeClassName().asString() +
                "." + CLASS_METADATA_FILE_EXTENSION
     }
 
-    platformStatic public fun getPackageFilePath(fqName: FqName): String =
-            packageFqNameToPath(fqName) + "/" + PACKAGE_FILE_NAME
+    public fun getPackageFilePath(fqName: FqName): String =
+            packageFqNameToPath(fqName) + "/" + shortName(fqName) + "." + PACKAGE_FILE_EXTENSION
+
+    public fun getStringTableFilePath(fqName: FqName): String =
+            packageFqNameToPath(fqName) + "/" + shortName(fqName) + "." + STRING_TABLE_FILE_EXTENSION
 
-    platformStatic public fun getStringTableFilePath(fqName: FqName): String =
-            packageFqNameToPath(fqName) + "/" + STRING_TABLE_FILE_NAME
 
     private fun packageFqNameToPath(fqName: FqName): String =
             fqName.asString().replace('.', '/')
+
+    private fun shortName(fqName: FqName): String =
+            if (fqName.isRoot()) "default-package" else fqName.shortName().asString()
 }
diff --git a/core/descriptors/src/org/jetbrains/kotlin/builtins/BuiltinsPackageFragment.kt b/core/descriptors/src/org/jetbrains/kotlin/builtins/BuiltinsPackageFragment.kt
index 0eb6093b304..2f679142c34 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/builtins/BuiltinsPackageFragment.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/builtins/BuiltinsPackageFragment.kt
@@ -36,7 +36,10 @@ public class BuiltinsPackageFragment(
         private val loadResource: (path: String) -> InputStream?
 ) : PackageFragmentDescriptorImpl(module, fqName) {
 
-    val nameResolver = NameResolver.read(loadResourceSure(BuiltInsSerializationUtil.getStringTableFilePath(fqName)))
+    val nameResolver = NameResolver.read(
+            loadResource(BuiltInsSerializationUtil.getStringTableFilePath(fqName))
+            ?: loadResourceSure(BuiltInsSerializationUtil.FallbackPaths.getStringTableFilePath(fqName))
+    )
 
     private var components: DeserializationComponents by Delegates.notNull()
 
@@ -46,7 +49,8 @@ public class BuiltinsPackageFragment(
     }
 
     private val memberScope = storageManager.createLazyValue {
-        val stream = loadResourceSure(BuiltInsSerializationUtil.getPackageFilePath(fqName))
+        val stream = loadResource(BuiltInsSerializationUtil.getPackageFilePath(fqName))
+                     ?: loadResourceSure(BuiltInsSerializationUtil.FallbackPaths.getPackageFilePath(fqName))
         val proto = ProtoBuf.Package.parseFrom(stream, BuiltInsSerializationUtil.EXTENSION_REGISTRY)
         DeserializedPackageMemberScope(this, proto, nameResolver, components, classNames = {
             proto.getExtension(BuiltInsProtoBuf.className)?.map { id -> nameResolver.getName(id) } ?: listOf()
diff --git a/js/js.serializer/src/org/jetbrains/kotlin/serialization/js/KotlinJavascriptSerializationUtil.kt b/js/js.serializer/src/org/jetbrains/kotlin/serialization/js/KotlinJavascriptSerializationUtil.kt
index d29de8f57f1..d57452142f2 100644
--- a/js/js.serializer/src/org/jetbrains/kotlin/serialization/js/KotlinJavascriptSerializationUtil.kt
+++ b/js/js.serializer/src/org/jetbrains/kotlin/serialization/js/KotlinJavascriptSerializationUtil.kt
@@ -117,12 +117,13 @@ public object KotlinJavascriptSerializationUtil {
         val fragments = module.getPackageFragmentProvider().getPackageFragments(fqName)
         val packageProto = serializer.packageProto(fragments, skip).build() ?: error("Package fragments not serialized: $fragments")
         packageProto.writeTo(packageStream)
-        writeFun(BuiltInsSerializationUtil.getPackageFilePath(fqName), packageStream)
+        // TODO: don't use fallback paths here
+        writeFun(BuiltInsSerializationUtil.FallbackPaths.getPackageFilePath(fqName), packageStream)
 
         val nameStream = ByteArrayOutputStream()
         val strings = serializer.getStringTable()
         SerializationUtil.serializeStringTable(nameStream, strings.serializeSimpleNames(), strings.serializeQualifiedNames())
-        writeFun(BuiltInsSerializationUtil.getStringTableFilePath(fqName), nameStream)
+        writeFun(BuiltInsSerializationUtil.FallbackPaths.getStringTableFilePath(fqName), nameStream)
     }
 
     fun getFileName(classDescriptor: ClassDescriptor): String {