diff --git a/kotlinx-coroutines-core/common/src/sync/Semaphore.kt b/kotlinx-coroutines-core/common/src/sync/Semaphore.kt
index b6ebc50..d72f989 100644
--- a/kotlinx-coroutines-core/common/src/sync/Semaphore.kt
+++ b/kotlinx-coroutines-core/common/src/sync/Semaphore.kt
@@ -1,3 +1,7 @@
+/*
+ * Copyright 2016-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
 package kotlinx.coroutines.sync
 
 import kotlinx.atomicfu.*
@@ -6,6 +10,7 @@
 import kotlin.coroutines.*
 import kotlin.jvm.*
 import kotlin.math.*
+import kotlin.native.concurrent.*
 
 /**
  * A counting semaphore for coroutines that logically maintains a number of available permits.