diff --git a/libraries/stdlib/jdk7/src/kotlin/io/path/PathReadWrite.kt b/libraries/stdlib/jdk7/src/kotlin/io/path/PathReadWrite.kt
index 20eab88422a..2ecd893accb 100644
--- a/libraries/stdlib/jdk7/src/kotlin/io/path/PathReadWrite.kt
+++ b/libraries/stdlib/jdk7/src/kotlin/io/path/PathReadWrite.kt
@@ -16,6 +16,7 @@ import java.nio.file.Files
 import java.nio.file.OpenOption
 import java.nio.file.Path
 import java.nio.file.StandardOpenOption
+import kotlin.contracts.*
 import kotlin.jvm.Throws
 
 /**
@@ -277,6 +278,9 @@ public inline fun Path.readLines(charset: Charset = Charsets.UTF_8): List<String
 @Throws(IOException::class)
 @kotlin.internal.InlineOnly
 public inline fun <T> Path.useLines(charset: Charset = Charsets.UTF_8, block: (Sequence<String>) -> T): T {
+    contract {
+        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
+    }
     return Files.newBufferedReader(this, charset).use { block(it.lineSequence()) }
 }
 
diff --git a/libraries/stdlib/jdk7/test/PathReadWriteTest.kt b/libraries/stdlib/jdk7/test/PathReadWriteTest.kt
index b45ecb2926c..e9ca1f5de9b 100644
--- a/libraries/stdlib/jdk7/test/PathReadWriteTest.kt
+++ b/libraries/stdlib/jdk7/test/PathReadWriteTest.kt
@@ -158,9 +158,13 @@ class PathReadWriteTest : AbstractPathTest() {
 
         assertEquals(listOf("Hello", "World"), file.readLines())
 
-        file.useLines {
-            assertEquals(listOf("Hello", "World"), it.toList())
+        val lines: List<String>
+        val linesResult = file.useLines {
+            lines = it.toList()
+            lines
         }
+        assertEquals(listOf("Hello", "World"), lines)
+        assertEquals(lines, linesResult)
 
         val text = file.inputStream().reader().readText()
         assertTrue("Hello" in text)
diff --git a/libraries/stdlib/jvm/src/kotlin/io/FileReadWrite.kt b/libraries/stdlib/jvm/src/kotlin/io/FileReadWrite.kt
index b5102f4b44e..115927dab6b 100644
--- a/libraries/stdlib/jvm/src/kotlin/io/FileReadWrite.kt
+++ b/libraries/stdlib/jvm/src/kotlin/io/FileReadWrite.kt
@@ -15,6 +15,8 @@ import java.util.*
 import java.nio.charset.Charset
 import java.nio.charset.CharsetEncoder
 import java.nio.charset.CodingErrorAction
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 import kotlin.math.ceil
 
 
@@ -279,5 +281,9 @@ public fun File.readLines(charset: Charset = Charsets.UTF_8): List<String> {
  * @param charset character set to use. By default uses UTF-8 charset.
  * @return the value returned by [block].
  */
-public inline fun <T> File.useLines(charset: Charset = Charsets.UTF_8, block: (Sequence<String>) -> T): T =
-    bufferedReader(charset).use { block(it.lineSequence()) }
+public inline fun <T> File.useLines(charset: Charset = Charsets.UTF_8, block: (Sequence<String>) -> T): T {
+    contract {
+        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
+    }
+    return bufferedReader(charset).use { block(it.lineSequence()) }
+}
diff --git a/libraries/stdlib/jvm/src/kotlin/io/ReadWrite.kt b/libraries/stdlib/jvm/src/kotlin/io/ReadWrite.kt
index 84358cbdfa5..372c94a2b5f 100644
--- a/libraries/stdlib/jvm/src/kotlin/io/ReadWrite.kt
+++ b/libraries/stdlib/jvm/src/kotlin/io/ReadWrite.kt
@@ -11,6 +11,8 @@ import java.io.*
 import java.nio.charset.Charset
 import java.net.URL
 import java.util.NoSuchElementException
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 import kotlin.internal.*
 
 
@@ -48,8 +50,12 @@ public fun Reader.readLines(): List<String> {
  * the processing is complete.
  * @return the value returned by [block].
  */
-public inline fun <T> Reader.useLines(block: (Sequence<String>) -> T): T =
-    buffered().use { block(it.lineSequence()) }
+public inline fun <T> Reader.useLines(block: (Sequence<String>) -> T): T {
+    contract {
+        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
+    }
+    return buffered().use { block(it.lineSequence()) }
+}
 
 /** Creates a new reader for the string. */
 @kotlin.internal.InlineOnly
diff --git a/libraries/stdlib/jvm/test/io/ReadWrite.kt b/libraries/stdlib/jvm/test/io/ReadWrite.kt
index fc57ed1fb49..89738f0a4c7 100644
--- a/libraries/stdlib/jvm/test/io/ReadWrite.kt
+++ b/libraries/stdlib/jvm/test/io/ReadWrite.kt
@@ -47,9 +47,13 @@ class ReadWriteTest {
 
         assertEquals(listOf("Hello", "World"), sample().readLines())
 
-        sample().useLines {
-            assertEquals(listOf("Hello", "World"), it.toList())
+        val lines: List<String>
+        val linesResult = sample().useLines {
+            lines = it.toList()
+            lines
         }
+        assertEquals(listOf("Hello", "World"), lines)
+        assertEquals(lines, linesResult)
 
 
         var reader = StringReader("")
@@ -94,9 +98,13 @@ class ReadWriteTest {
 
         assertEquals(arrayListOf("Hello", "World"), file.readLines())
 
-        file.useLines {
-            assertEquals(arrayListOf("Hello", "World"), it.toList())
+        val lines: List<String>
+        val linesResult = file.useLines {
+            lines = it.toList()
+            lines
         }
+        assertEquals(listOf("Hello", "World"), lines)
+        assertEquals(lines, linesResult)
 
         val text = file.inputStream().reader().readText()
         assertTrue(text.contains("Hello"))