diff --git a/akka-stream-tests/src/test/scala/akka/stream/io/FileSinkSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/io/FileSinkSpec.scala
index c527f51fb6..a6f57b977c 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/io/FileSinkSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/io/FileSinkSpec.scala
@@ -65,7 +65,26 @@ class FileSinkSpec extends StreamSpec(UnboundedMailboxConfig) {
       }, create = false)
     }
 
-    "by default write into existing file" in assertAllStagesStopped {
+    "write into existing file without wiping existing data" in assertAllStagesStopped {
+      targetFile { f ⇒
+        def write(lines: List[String]) =
+          Source(lines)
+            .map(ByteString(_))
+            .runWith(FileIO.toPath(f, Set(StandardOpenOption.WRITE, StandardOpenOption.CREATE)))
+
+        val completion1 = write(TestLines)
+        Await.result(completion1, 3.seconds)
+
+        val lastWrite = List("x" * 100)
+        val completion2 = write(lastWrite)
+        val result = Await.result(completion2, 3.seconds)
+
+        result.count should ===(lastWrite.flatten.length)
+        checkFileContents(f, lastWrite.mkString("") + TestLines.mkString("").drop(100))
+      }
+    }
+
+    "by default replace the existing file" in assertAllStagesStopped {
       targetFile { f ⇒
         def write(lines: List[String]) =
           Source(lines)
@@ -80,7 +99,7 @@ class FileSinkSpec extends StreamSpec(UnboundedMailboxConfig) {
         val result = Await.result(completion2, 3.seconds)
 
         result.count should ===(lastWrite.flatten.length)
-        checkFileContents(f, lastWrite.mkString("") + TestLines.mkString("").drop(100))
+        checkFileContents(f, lastWrite.mkString(""))
       }
     }
 
diff --git a/akka-stream/src/main/scala/akka/stream/javadsl/FileIO.scala b/akka-stream/src/main/scala/akka/stream/javadsl/FileIO.scala
index 4e0fd2bba8..ad2a1f70a0 100644
--- a/akka-stream/src/main/scala/akka/stream/javadsl/FileIO.scala
+++ b/akka-stream/src/main/scala/akka/stream/javadsl/FileIO.scala
@@ -8,7 +8,7 @@ import java.nio.file.{ OpenOption, Path }
 import java.util
 import java.util.concurrent.CompletionStage
 
-import akka.stream.{ IOResult, javadsl, scaladsl }
+import akka.stream.{ ActorAttributes, IOResult, javadsl, scaladsl }
 import akka.util.ByteString
 
 import scala.collection.JavaConverters._
@@ -20,7 +20,8 @@ object FileIO {
 
   /**
    * Creates a Sink that writes incoming [[ByteString]] elements to the given file.
-   * Overwrites existing files, if you want to append to an existing file use [[#file(Path, util.Set[OpenOption])]].
+   * Overwrites existing files by truncating their contents, if you want to append to an existing file use
+   * [[#toFile(File, util.Set[OpenOption])]] with [[java.nio.file.StandardOpenOption.APPEND]].
    *
    * Materializes a [[java.util.concurrent.CompletionStage]] of [[IOResult]] that will be completed with the size of the file (in bytes) at the streams completion,
    * and a possible exception if IO operation was not completed successfully.
@@ -35,7 +36,8 @@ object FileIO {
 
   /**
    * Creates a Sink that writes incoming [[ByteString]] elements to the given file path.
-   * Overwrites existing files, if you want to append to an existing file use [[#file(Path, util.Set[OpenOption])]].
+   * Overwrites existing files by truncating their contents, if you want to append to an existing file
+   * [[#toPath(Path, util.Set[OpenOption])]] with [[java.nio.file.StandardOpenOption.APPEND]].
    *
    * Materializes a [[java.util.concurrent.CompletionStage]] of [[IOResult]] that will be completed with the size of the file (in bytes) at the streams completion,
    * and a possible exception if IO operation was not completed successfully.
@@ -58,7 +60,7 @@ object FileIO {
    * set it for a given Source by using [[ActorAttributes]].
    *
    * @param f The file to write to
-   * @param options File open options
+   * @param options File open options, see [[java.nio.file.StandardOpenOption]]
    */
   @deprecated("Use `toPath` instead.", "2.4.5")
   def toFile[Opt <: OpenOption](f: File, options: util.Set[Opt]): javadsl.Sink[ByteString, CompletionStage[IOResult]] =
@@ -74,7 +76,7 @@ object FileIO {
    * set it for a given Source by using [[ActorAttributes]].
    *
    * @param f The file path to write to
-   * @param options File open options
+   * @param options File open options, see [[java.nio.file.StandardOpenOption]]
    */
   def toPath[Opt <: OpenOption](f: Path, options: util.Set[Opt]): javadsl.Sink[ByteString, CompletionStage[IOResult]] =
     new Sink(scaladsl.FileIO.toPath(f, options.asScala.toSet).toCompletionStage())
@@ -89,7 +91,7 @@ object FileIO {
    * set it for a given Source by using [[ActorAttributes]].
    *
    * @param f The file path to write to
-   * @param options File open options
+   * @param options File open options, see [[java.nio.file.StandardOpenOption]]
    * @param startPosition startPosition the start position to read from, defaults to 0
    */
   def toPath[Opt <: OpenOption](f: Path, options: util.Set[Opt], startPosition: Long): javadsl.Sink[ByteString, CompletionStage[IOResult]] =
diff --git a/akka-stream/src/main/scala/akka/stream/scaladsl/FileIO.scala b/akka-stream/src/main/scala/akka/stream/scaladsl/FileIO.scala
index 81b6fbe0b7..64b640f037 100644
--- a/akka-stream/src/main/scala/akka/stream/scaladsl/FileIO.scala
+++ b/akka-stream/src/main/scala/akka/stream/scaladsl/FileIO.scala
@@ -9,7 +9,7 @@ import java.nio.file.StandardOpenOption._
 
 import akka.stream.impl.Stages.DefaultAttributes
 import akka.stream.impl.io._
-import akka.stream.IOResult
+import akka.stream.{ ActorAttributes, IOResult }
 import akka.util.ByteString
 
 import scala.concurrent.Future
@@ -76,7 +76,8 @@ object FileIO {
     Source.fromGraph(new FileSource(f, chunkSize, startPosition, DefaultAttributes.fileSource, sourceShape("FileSource")))
 
   /**
-   * Creates a Sink which writes incoming [[ByteString]] elements to the given file. Overwrites existing files by default.
+   * Creates a Sink which writes incoming [[ByteString]] elements to the given file. Overwrites existing files
+   * by truncating their contents as default.
    *
    * Materializes a [[Future]] of [[IOResult]] that will be completed with the size of the file (in bytes) at the streams completion,
    * and a possible exception if IO operation was not completed successfully.
@@ -85,14 +86,15 @@ object FileIO {
    * unless configured otherwise by using [[akka.stream.ActorAttributes]].
    *
    * @param f the file to write to
-   * @param options File open options, defaults to Set(WRITE, CREATE)
+   * @param options File open options, see [[java.nio.file.StandardOpenOption]], defaults to Set(WRITE, TRUNCATE_EXISTING, CREATE)
    */
   @deprecated("Use `toPath` instead", "2.4.5")
-  def toFile(f: File, options: Set[OpenOption] = Set(WRITE, CREATE)): Sink[ByteString, Future[IOResult]] =
+  def toFile(f: File, options: Set[OpenOption] = Set(WRITE, TRUNCATE_EXISTING, CREATE)): Sink[ByteString, Future[IOResult]] =
     toPath(f.toPath, options)
 
   /**
-   * Creates a Sink which writes incoming [[ByteString]] elements to the given file path. Overwrites existing files by default.
+   * Creates a Sink which writes incoming [[ByteString]] elements to the given file path. Overwrites existing files
+   * by truncating their contents as default.
    *
    * Materializes a [[Future]] of [[IOResult]] that will be completed with the size of the file (in bytes) at the streams completion,
    * and a possible exception if IO operation was not completed successfully.
@@ -101,13 +103,14 @@ object FileIO {
    * unless configured otherwise by using [[akka.stream.ActorAttributes]].
    *
    * @param f the file path to write to
-   * @param options File open options, defaults to Set(WRITE, CREATE)
+   * @param options File open options, see [[java.nio.file.StandardOpenOption]], defaults to Set(WRITE, TRUNCATE_EXISTING, CREATE)
    */
-  def toPath(f: Path, options: Set[OpenOption] = Set(WRITE, CREATE)): Sink[ByteString, Future[IOResult]] =
+  def toPath(f: Path, options: Set[OpenOption] = Set(WRITE, TRUNCATE_EXISTING, CREATE)): Sink[ByteString, Future[IOResult]] =
     toPath(f, options, startPosition = 0)
 
   /**
-   * Creates a Sink which writes incoming [[ByteString]] elements to the given file path. Overwrites existing files by default.
+   * Creates a Sink which writes incoming [[ByteString]] elements to the given file path. Overwrites existing files
+   * by truncating their contents as default.
    *
    * Materializes a [[Future]] of [[IOResult]] that will be completed with the size of the file (in bytes) at the streams completion,
    * and a possible exception if IO operation was not completed successfully.
@@ -116,7 +119,7 @@ object FileIO {
    * unless configured otherwise by using [[ActorAttributes]].
    *
    * @param f the file path to write to
-   * @param options File open options, defaults to Set(WRITE, CREATE)
+   * @param options File open options, see [[java.nio.file.StandardOpenOption]], defaults to Set(WRITE, CREATE)
    * @param startPosition the start position to write to
    */
   def toPath(f: Path, options: Set[OpenOption], startPosition: Long): Sink[ByteString, Future[IOResult]] =