diff --git a/libraries/kotlin.test/common/src/main/kotlin/kotlin/test/AssertionsH.kt b/libraries/kotlin.test/common/src/main/kotlin/kotlin/test/AssertionsH.kt
index 5c1cd282408..610b0ae17e0 100644
--- a/libraries/kotlin.test/common/src/main/kotlin/kotlin/test/AssertionsH.kt
+++ b/libraries/kotlin.test/common/src/main/kotlin/kotlin/test/AssertionsH.kt
@@ -6,7 +6,7 @@ import kotlin.reflect.KClass
  * Comments out a block of test code until it is implemented while keeping a link to the code
  * to implement in your unit test output
  */
-header fun todo(block: () -> Unit)
+expect fun todo(block: () -> Unit)
 
 /** Asserts that a [block] fails with a specific exception of type [exceptionClass] being thrown. */
-header fun <T : Throwable> assertFailsWith(exceptionClass: KClass<T>, message: String?, block: () -> Unit): T
+expect fun <T : Throwable> assertFailsWith(exceptionClass: KClass<T>, message: String?, block: () -> Unit): T
diff --git a/libraries/kotlin.test/common/src/main/kotlin/kotlin/test/Utils.kt b/libraries/kotlin.test/common/src/main/kotlin/kotlin/test/Utils.kt
index c808b3d5d66..99e80dc56db 100644
--- a/libraries/kotlin.test/common/src/main/kotlin/kotlin/test/Utils.kt
+++ b/libraries/kotlin.test/common/src/main/kotlin/kotlin/test/Utils.kt
@@ -1,7 +1,7 @@
 package kotlin.test
 
 internal fun messagePrefix(message: String?) = if (message == null) "" else "$message. "
-internal header fun lookupAsserter(): Asserter
+internal expect fun lookupAsserter(): Asserter
 
 @PublishedApi // required to get stable name as it's called from box tests
 internal fun overrideAsserter(value: Asserter?): Asserter? {
diff --git a/libraries/kotlin.test/common/src/main/kotlin/org/junit/Test.kt b/libraries/kotlin.test/common/src/main/kotlin/org/junit/Test.kt
index 31460f5c959..53f5c6f165e 100644
--- a/libraries/kotlin.test/common/src/main/kotlin/org/junit/Test.kt
+++ b/libraries/kotlin.test/common/src/main/kotlin/org/junit/Test.kt
@@ -1,4 +1,4 @@
 package org.junit
 
 @Suppress("NO_ACTUAL_FOR_EXPECT")
-header annotation class Test
+expect annotation class Test
diff --git a/libraries/stdlib/common/src/kotlin/CollectionsH.kt b/libraries/stdlib/common/src/kotlin/CollectionsH.kt
index 29617da361b..dad4d73da23 100644
--- a/libraries/stdlib/common/src/kotlin/CollectionsH.kt
+++ b/libraries/stdlib/common/src/kotlin/CollectionsH.kt
@@ -16,7 +16,7 @@
 
 package kotlin.collections
 
-open header class ArrayList<E> : MutableList<E> {
+open expect class ArrayList<E> : MutableList<E> {
     constructor(capacity: Int)
     constructor()
     constructor(c: Collection<E>)
@@ -52,7 +52,7 @@ open header class ArrayList<E> : MutableList<E> {
     override fun subList(fromIndex: Int, toIndex: Int): MutableList<E>
 }
 
-open header class HashMap<K, V> : MutableMap<K, V> {
+open expect class HashMap<K, V> : MutableMap<K, V> {
     constructor()
     constructor(initialCapacity: Int)
     constructor(initialCapacity: Int, loadFactor: Float)
@@ -75,14 +75,14 @@ open header class HashMap<K, V> : MutableMap<K, V> {
     override val entries: MutableSet<MutableMap.MutableEntry<K, V>>
 }
 
-open header class LinkedHashMap<K, V> : HashMap<K, V> {
+open expect class LinkedHashMap<K, V> : HashMap<K, V> {
     constructor()
     constructor(initialCapacity: Int)
     constructor(initialCapacity: Int, loadFactor: Float)
     constructor(original: Map<out K, V>)
 }
 
-open header class HashSet<E> : MutableSet<E> {
+open expect class HashSet<E> : MutableSet<E> {
     constructor()
     constructor(initialCapacity: Int)
     constructor(initialCapacity: Int, loadFactor: Float)
@@ -104,17 +104,17 @@ open header class HashSet<E> : MutableSet<E> {
     override fun clear()
 }
 
-open header class LinkedHashSet<E> : HashSet<E> {
+open expect class LinkedHashSet<E> : HashSet<E> {
     constructor()
     constructor(initialCapacity: Int)
     constructor(initialCapacity: Int, loadFactor: Float)
     constructor(c: Collection<E>)
 }
 
-header interface RandomAccess
+expect interface RandomAccess
 
 
-header abstract class AbstractMutableList<E> : MutableList<E> {
+expect abstract class AbstractMutableList<E> : MutableList<E> {
     protected constructor()
 
     // From List
@@ -144,19 +144,19 @@ header abstract class AbstractMutableList<E> : MutableList<E> {
 // From collections.kt
 
 /** Returns the array if it's not `null`, or an empty array otherwise. */
-header inline fun <reified T> Array<out T>?.orEmpty(): Array<out T>
+expect inline fun <reified T> Array<out T>?.orEmpty(): Array<out T>
 
 
-header inline fun <reified T> Collection<T>.toTypedArray(): Array<T>
+expect inline fun <reified T> Collection<T>.toTypedArray(): Array<T>
 
-header fun <T : Comparable<T>> MutableList<T>.sort(): Unit
-header fun <T> MutableList<T>.sortWith(comparator: Comparator<in T>): Unit
+expect fun <T : Comparable<T>> MutableList<T>.sort(): Unit
+expect fun <T> MutableList<T>.sortWith(comparator: Comparator<in T>): Unit
 
 
 // from Grouping.kt
-public header fun <T, K> Grouping<T, K>.eachCount(): Map<K, Int>
-// public header inline fun <T, K> Grouping<T, K>.eachSumOf(valueSelector: (T) -> Int): Map<K, Int>
+public expect fun <T, K> Grouping<T, K>.eachCount(): Map<K, Int>
+// public expect inline fun <T, K> Grouping<T, K>.eachSumOf(valueSelector: (T) -> Int): Map<K, Int>
 
-internal header fun copyToArrayImpl(collection: Collection<*>): Array<Any?>
+internal expect fun copyToArrayImpl(collection: Collection<*>): Array<Any?>
 
-internal header fun <T> copyToArrayImpl(collection: Collection<*>, array: Array<T>): Array<T>
+internal expect fun <T> copyToArrayImpl(collection: Collection<*>, array: Array<T>): Array<T>
diff --git a/libraries/stdlib/common/src/kotlin/ConsoleH.kt b/libraries/stdlib/common/src/kotlin/ConsoleH.kt
index aa57572dff0..6b976c0e66c 100644
--- a/libraries/stdlib/common/src/kotlin/ConsoleH.kt
+++ b/libraries/stdlib/common/src/kotlin/ConsoleH.kt
@@ -2,10 +2,10 @@ package kotlin.io
 
 
 /** Prints a newline to the standard output stream. */
-public header fun println()
+public expect fun println()
 
 /** Prints the given message and newline to the standard output stream. */
-public header fun println(message: Any?)
+public expect fun println(message: Any?)
 
 /** Prints the given message to the standard output stream. */
-public header fun print(message: Any?)
+public expect fun print(message: Any?)
diff --git a/libraries/stdlib/common/src/kotlin/CoroutinesH.kt b/libraries/stdlib/common/src/kotlin/CoroutinesH.kt
index c88a7fe7e1b..74cc6332dd1 100644
--- a/libraries/stdlib/common/src/kotlin/CoroutinesH.kt
+++ b/libraries/stdlib/common/src/kotlin/CoroutinesH.kt
@@ -1,7 +1,7 @@
 package kotlin.coroutines.experimental
 
 @PublishedApi
-internal header class SafeContinuation<in T> : Continuation<T> {
+internal expect class SafeContinuation<in T> : Continuation<T> {
     internal constructor(delegate: Continuation<T>, initialResult: Any?)
 
     @PublishedApi
diff --git a/libraries/stdlib/common/src/kotlin/CoroutinesIntrinsicsH.kt b/libraries/stdlib/common/src/kotlin/CoroutinesIntrinsicsH.kt
index 0cc510533eb..b0121e11281 100644
--- a/libraries/stdlib/common/src/kotlin/CoroutinesIntrinsicsH.kt
+++ b/libraries/stdlib/common/src/kotlin/CoroutinesIntrinsicsH.kt
@@ -26,7 +26,7 @@ import kotlin.coroutines.experimental.Continuation
  * coroutine using a reference to the suspending function.
  */
 @SinceKotlin("1.1")
-public header inline fun <T> (suspend () -> T).startCoroutineUninterceptedOrReturn(
+public expect inline fun <T> (suspend () -> T).startCoroutineUninterceptedOrReturn(
         completion: Continuation<T>
 ): Any?
 
@@ -38,18 +38,18 @@ public header inline fun <T> (suspend () -> T).startCoroutineUninterceptedOrRetu
  * coroutine using a reference to the suspending function.
  */
 @SinceKotlin("1.1")
-public header inline fun <R, T> (suspend R.() -> T).startCoroutineUninterceptedOrReturn(
+public expect inline fun <R, T> (suspend R.() -> T).startCoroutineUninterceptedOrReturn(
         receiver: R,
         completion: Continuation<T>
 ): Any?
 
 @SinceKotlin("1.1")
-public header fun <T> (suspend () -> T).createCoroutineUnchecked(
+public expect fun <T> (suspend () -> T).createCoroutineUnchecked(
         completion: Continuation<T>
 ): Continuation<Unit>
 
 @SinceKotlin("1.1")
-public header fun <R, T> (suspend R.() -> T).createCoroutineUnchecked(
+public expect fun <R, T> (suspend R.() -> T).createCoroutineUnchecked(
         receiver: R,
         completion: Continuation<T>
 ): Continuation<Unit>
diff --git a/libraries/stdlib/common/src/kotlin/JvmAnnotationsH.kt b/libraries/stdlib/common/src/kotlin/JvmAnnotationsH.kt
index 6e8a8842817..373e280241b 100644
--- a/libraries/stdlib/common/src/kotlin/JvmAnnotationsH.kt
+++ b/libraries/stdlib/common/src/kotlin/JvmAnnotationsH.kt
@@ -3,9 +3,9 @@ package kotlin.jvm
 import kotlin.annotation.AnnotationTarget.*
 
 @Target(FUNCTION, PROPERTY_GETTER, PROPERTY_SETTER, FILE)
-header annotation class JvmName(val name: String)
+expect annotation class JvmName(val name: String)
 
 @Target(FILE)
-header annotation class JvmMultifileClass
+expect annotation class JvmMultifileClass
 
-header annotation class JvmField
+expect annotation class JvmField
diff --git a/libraries/stdlib/common/src/kotlin/KotlinH.kt b/libraries/stdlib/common/src/kotlin/KotlinH.kt
index 1674d90ffdb..847ea95b798 100644
--- a/libraries/stdlib/common/src/kotlin/KotlinH.kt
+++ b/libraries/stdlib/common/src/kotlin/KotlinH.kt
@@ -18,101 +18,101 @@ package kotlin
 
 import kotlin.annotation.AnnotationTarget.*
 
-open header class Error : Throwable {
+open expect class Error : Throwable {
     constructor()
     constructor(message: String)
 }
 
-open header class Exception : Throwable {
+open expect class Exception : Throwable {
     constructor()
     constructor(message: String)
 }
 
-open header class IllegalArgumentException : RuntimeException {
+open expect class IllegalArgumentException : RuntimeException {
     constructor()
     constructor(message: String)
 }
 
-open header class IllegalStateException : RuntimeException {
+open expect class IllegalStateException : RuntimeException {
     constructor()
     constructor(message: String)
 }
 
-open header class IndexOutOfBoundsException : RuntimeException {
+open expect class IndexOutOfBoundsException : RuntimeException {
     constructor()
     constructor(message: String)
 }
 
-open header class NoSuchElementException : RuntimeException {
+open expect class NoSuchElementException : RuntimeException {
     constructor()
     constructor(message: String)
 }
 
-open header class RuntimeException : Exception {
+open expect class RuntimeException : Exception {
     constructor()
     constructor(message: String)
 }
 
-open header class UnsupportedOperationException : RuntimeException {
+open expect class UnsupportedOperationException : RuntimeException {
     constructor()
     constructor(message: String)
 }
 
 // TODO: Provide typealias impl in stdlib-jvm
-open header class AssertionError : Error {
+open expect class AssertionError : Error {
     constructor()
     constructor(message: String)
 }
 
 
-header interface Comparator<T> {
+expect interface Comparator<T> {
     fun compare(a: T, b: T): Int
 }
 
-header inline fun <T> Comparator(crossinline comparison: (a: T, b: T) -> Int): Comparator<T>
+expect inline fun <T> Comparator(crossinline comparison: (a: T, b: T) -> Int): Comparator<T>
 
 // From kotlin.kt
 
-internal header fun <T> arrayOfNulls(reference: Array<out T>, size: Int): Array<T>
-internal inline header fun <K, V> Map<K, V>.toSingletonMapOrSelf(): Map<K, V>
-internal inline header fun <K, V> Map<out K, V>.toSingletonMap(): Map<K, V>
-internal inline header fun <T> Array<out T>.copyToArrayOfAny(isVarargs: Boolean): Array<out Any?>
+internal expect fun <T> arrayOfNulls(reference: Array<out T>, size: Int): Array<T>
+internal inline expect fun <K, V> Map<K, V>.toSingletonMapOrSelf(): Map<K, V>
+internal inline expect fun <K, V> Map<out K, V>.toSingletonMap(): Map<K, V>
+internal inline expect fun <T> Array<out T>.copyToArrayOfAny(isVarargs: Boolean): Array<out Any?>
 
-internal header interface Serializable
+internal expect interface Serializable
 
 // From numbers.kt
 
-header fun Double.isNaN(): Boolean
-header fun Float.isNaN(): Boolean
-header fun Double.isInfinite(): Boolean
-header fun Float.isInfinite(): Boolean
-header fun Double.isFinite(): Boolean
-header fun Float.isFinite(): Boolean
+expect fun Double.isNaN(): Boolean
+expect fun Float.isNaN(): Boolean
+expect fun Double.isInfinite(): Boolean
+expect fun Float.isInfinite(): Boolean
+expect fun Double.isFinite(): Boolean
+expect fun Float.isFinite(): Boolean
 
 
 // From concurrent.kt
 
 @Target(PROPERTY, FIELD)
-header annotation class Volatile
+expect annotation class Volatile
 
-inline header fun <R> synchronized(lock: Any, crossinline block: () -> R): R
+inline expect fun <R> synchronized(lock: Any, crossinline block: () -> R): R
 
 
 
 
 // from lazy.kt
 
-public header fun <T> lazy(initializer: () -> T): Lazy<T>
+public expect fun <T> lazy(initializer: () -> T): Lazy<T>
 
 /**
  * Creates a new instance of the [Lazy] that uses the specified initialization function [initializer].
  *
  * The [mode] parameter is ignored. */
-public header fun <T> lazy(mode: LazyThreadSafetyMode, initializer: () -> T): Lazy<T>
+public expect fun <T> lazy(mode: LazyThreadSafetyMode, initializer: () -> T): Lazy<T>
 
 /**
  * Creates a new instance of the [Lazy] that uses the specified initialization function [initializer].
  *
  * The [lock] parameter is ignored.
  */
-public header fun <T> lazy(lock: Any?, initializer: () -> T): Lazy<T>
+public expect fun <T> lazy(lock: Any?, initializer: () -> T): Lazy<T>
diff --git a/libraries/stdlib/common/src/kotlin/SequencesH.kt b/libraries/stdlib/common/src/kotlin/SequencesH.kt
index 54bb012610f..03b3767aa75 100644
--- a/libraries/stdlib/common/src/kotlin/SequencesH.kt
+++ b/libraries/stdlib/common/src/kotlin/SequencesH.kt
@@ -1,6 +1,6 @@
 package kotlin.sequences
 
-internal header class ConstrainedOnceSequence<T> : Sequence<T> {
+internal expect class ConstrainedOnceSequence<T> : Sequence<T> {
     constructor(sequence: Sequence<T>)
 
     override fun iterator(): Iterator<T>
diff --git a/libraries/stdlib/common/src/kotlin/TextH.kt b/libraries/stdlib/common/src/kotlin/TextH.kt
index f0f8020cad4..928dad577f9 100644
--- a/libraries/stdlib/common/src/kotlin/TextH.kt
+++ b/libraries/stdlib/common/src/kotlin/TextH.kt
@@ -16,13 +16,13 @@
 
 package kotlin.text
 
-header interface Appendable {
+expect interface Appendable {
     fun append(c: Char): Appendable
     fun append(csq: CharSequence?): Appendable
     fun append(csq: CharSequence?, start: Int, end: Int): Appendable
 }
 
-header class StringBuilder : Appendable, CharSequence {
+expect class StringBuilder : Appendable, CharSequence {
     constructor()
     constructor(capacity: Int)
     constructor(seq: CharSequence)
@@ -38,7 +38,7 @@ header class StringBuilder : Appendable, CharSequence {
     fun append(obj: Any?): StringBuilder
 }
 
-header class Regex {
+expect class Regex {
     constructor(pattern: String)
     constructor(pattern: String, option: RegexOption)
     constructor(pattern: String, options: Set<RegexOption>)
@@ -65,11 +65,11 @@ header class Regex {
     }
 }
 
-header class MatchGroup {
+expect class MatchGroup {
     val value: String
 }
 
-header enum class RegexOption {
+expect enum class RegexOption {
     IGNORE_CASE,
     MULTILINE
 }
@@ -77,50 +77,50 @@ header enum class RegexOption {
 
 // From char.kt
 
-header fun Char.isWhitespace(): Boolean
-header fun Char.toLowerCase(): Char
-header fun Char.toUpperCase(): Char
-header fun Char.isHighSurrogate(): Boolean
-header fun Char.isLowSurrogate(): Boolean
+expect fun Char.isWhitespace(): Boolean
+expect fun Char.toLowerCase(): Char
+expect fun Char.toUpperCase(): Char
+expect fun Char.isHighSurrogate(): Boolean
+expect fun Char.isLowSurrogate(): Boolean
 
 // From string.kt
 
-internal header fun String.nativeIndexOf(str: String, fromIndex: Int): Int
-internal header fun String.nativeLastIndexOf(str: String, fromIndex: Int): Int
-internal header fun String.nativeStartsWith(s: String, position: Int): Boolean
-internal header fun String.nativeEndsWith(s: String): Boolean
+internal expect fun String.nativeIndexOf(str: String, fromIndex: Int): Int
+internal expect fun String.nativeLastIndexOf(str: String, fromIndex: Int): Int
+internal expect fun String.nativeStartsWith(s: String, position: Int): Boolean
+internal expect fun String.nativeEndsWith(s: String): Boolean
 
 
-public header fun String.substring(startIndex: Int): String
-public header fun String.substring(startIndex: Int, endIndex: Int): String
+public expect fun String.substring(startIndex: Int): String
+public expect fun String.substring(startIndex: Int, endIndex: Int): String
 
 
-public header inline fun String.toUpperCase(): String
-public header inline fun String.toLowerCase(): String
-public header inline fun String.capitalize(): String
-public header inline fun String.decapitalize(): String
-public header fun CharSequence.repeat(n: Int): String
+public expect inline fun String.toUpperCase(): String
+public expect inline fun String.toLowerCase(): String
+public expect inline fun String.capitalize(): String
+public expect inline fun String.decapitalize(): String
+public expect fun CharSequence.repeat(n: Int): String
 
 
 // TOOD: requires optional parameters (and named!)
-header fun String.replace(oldChar: Char, newChar: Char): String
-header fun String.replace(oldChar: Char, newChar: Char, ignoreCase: Boolean): String
-header fun String.replace(oldValue: String, newValue: String): String
-header fun String.replace(oldValue: String, newValue: String, ignoreCase: Boolean): String
-header fun String.replaceFirst(oldChar: Char, newChar: Char): String
-header fun String.replaceFirst(oldChar: Char, newChar: Char, ignoreCase: Boolean): String
-header fun String.replaceFirst(oldValue: String, newValue: String): String
-header fun String.replaceFirst(oldValue: String, newValue: String, ignoreCase: Boolean): String
-header fun String?.equals(other: String?): Boolean
-header fun String?.equals(other: String?, ignoreCase: Boolean): Boolean
+expect fun String.replace(oldChar: Char, newChar: Char): String
+expect fun String.replace(oldChar: Char, newChar: Char, ignoreCase: Boolean): String
+expect fun String.replace(oldValue: String, newValue: String): String
+expect fun String.replace(oldValue: String, newValue: String, ignoreCase: Boolean): String
+expect fun String.replaceFirst(oldChar: Char, newChar: Char): String
+expect fun String.replaceFirst(oldChar: Char, newChar: Char, ignoreCase: Boolean): String
+expect fun String.replaceFirst(oldValue: String, newValue: String): String
+expect fun String.replaceFirst(oldValue: String, newValue: String, ignoreCase: Boolean): String
+expect fun String?.equals(other: String?): Boolean
+expect fun String?.equals(other: String?, ignoreCase: Boolean): Boolean
 
 // From stringsCode.kt
 
-internal inline header fun String.nativeIndexOf(ch: Char, fromIndex: Int): Int
-internal inline header fun String.nativeLastIndexOf(ch: Char, fromIndex: Int): Int
+internal inline expect fun String.nativeIndexOf(ch: Char, fromIndex: Int): Int
+internal inline expect fun String.nativeLastIndexOf(ch: Char, fromIndex: Int): Int
 
-header fun CharSequence.isBlank(): Boolean
-header fun CharSequence.regionMatches(thisOffset: Int, other: CharSequence, otherOffset: Int, length: Int, ignoreCase: Boolean): Boolean
+expect fun CharSequence.isBlank(): Boolean
+expect fun CharSequence.regionMatches(thisOffset: Int, other: CharSequence, otherOffset: Int, length: Int, ignoreCase: Boolean): Boolean
 
 
 
@@ -128,76 +128,76 @@ header fun CharSequence.regionMatches(thisOffset: Int, other: CharSequence, othe
  * Parses the string as a signed [Byte] number and returns the result.
  * @throws NumberFormatException if the string is not a valid representation of a number.
  */
-header fun String.toByte(): Byte
+expect fun String.toByte(): Byte
 
 /**
  * Parses the string as a signed [Byte] number and returns the result.
  * @throws NumberFormatException if the string is not a valid representation of a number.
  */
-header fun String.toByte(radix: Int): Byte
+expect fun String.toByte(radix: Int): Byte
 
 
 /**
  * Parses the string as a [Short] number and returns the result.
  * @throws NumberFormatException if the string is not a valid representation of a number.
  */
-header fun String.toShort(): Short
+expect fun String.toShort(): Short
 
 /**
  * Parses the string as a [Short] number and returns the result.
  * @throws NumberFormatException if the string is not a valid representation of a number.
  */
-header fun String.toShort(radix: Int): Short
+expect fun String.toShort(radix: Int): Short
 
 /**
  * Parses the string as an [Int] number and returns the result.
  * @throws NumberFormatException if the string is not a valid representation of a number.
  */
-header fun String.toInt(): Int
+expect fun String.toInt(): Int
 
 /**
  * Parses the string as an [Int] number and returns the result.
  * @throws NumberFormatException if the string is not a valid representation of a number.
  */
-header fun String.toInt(radix: Int): Int
+expect fun String.toInt(radix: Int): Int
 
 /**
  * Parses the string as a [Long] number and returns the result.
  * @throws NumberFormatException if the string is not a valid representation of a number.
  */
-header fun String.toLong(): Long
+expect fun String.toLong(): Long
 
 /**
  * Parses the string as a [Long] number and returns the result.
  * @throws NumberFormatException if the string is not a valid representation of a number.
  */
-header fun String.toLong(radix: Int): Long
+expect fun String.toLong(radix: Int): Long
 
 /**
  * Parses the string as a [Double] number and returns the result.
  * @throws NumberFormatException if the string is not a valid representation of a number.
  */
-header fun String.toDouble(): Double
+expect fun String.toDouble(): Double
 
 /**
  * Parses the string as a [Float] number and returns the result.
  * @throws NumberFormatException if the string is not a valid representation of a number.
  */
-header fun String.toFloat(): Float
+expect fun String.toFloat(): Float
 
 /**
  * Parses the string as a [Double] number and returns the result
  * or `null` if the string is not a valid representation of a number.
  */
-header fun String.toDoubleOrNull(): Double?
+expect fun String.toDoubleOrNull(): Double?
 
 /**
  * Parses the string as a [Float] number and returns the result
  * or `null` if the string is not a valid representation of a number.
  */
-header fun String.toFloatOrNull(): Float?
+expect fun String.toFloatOrNull(): Float?
 
 
 @PublishedApi
-internal header fun checkRadix(radix: Int): Int
-internal header fun digitOf(char: Char, radix: Int): Int
+internal expect fun checkRadix(radix: Int): Int
+internal expect fun digitOf(char: Char, radix: Int): Int
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/multiplatformProject/lib/src/main/kotlin/PlatformClass.kt b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/multiplatformProject/lib/src/main/kotlin/PlatformClass.kt
index 405238ed8b7..526586c399e 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/multiplatformProject/lib/src/main/kotlin/PlatformClass.kt
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/multiplatformProject/lib/src/main/kotlin/PlatformClass.kt
@@ -1,6 +1,6 @@
 package foo
 
-header class PlatformClass {
+expect class PlatformClass {
     val value: String
 }
 
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/multiplatformProject/lib/src/test/kotlin/PlatformTest.kt b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/multiplatformProject/lib/src/test/kotlin/PlatformTest.kt
index f6da234ab3e..2688286a168 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/multiplatformProject/lib/src/test/kotlin/PlatformTest.kt
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/multiplatformProject/lib/src/test/kotlin/PlatformTest.kt
@@ -1,6 +1,6 @@
 package foo
 
-header class PlatformTest {
+expect class PlatformTest {
     val value: PlatformClass
 }
 
diff --git a/libraries/tools/kotlin-maven-plugin-test/src/it/test-multiplatform/shared/src/main/kotlin/org/jetbrains/api.kt b/libraries/tools/kotlin-maven-plugin-test/src/it/test-multiplatform/shared/src/main/kotlin/org/jetbrains/api.kt
index f881a47de90..5d9dcf70a38 100644
--- a/libraries/tools/kotlin-maven-plugin-test/src/it/test-multiplatform/shared/src/main/kotlin/org/jetbrains/api.kt
+++ b/libraries/tools/kotlin-maven-plugin-test/src/it/test-multiplatform/shared/src/main/kotlin/org/jetbrains/api.kt
@@ -1,6 +1,6 @@
 package org.jetbrains
 
-header fun doMain()
+expect fun doMain()
 
 fun getGreeting() : String {
     return "Hello, World!"