diff --git a/akka-http-core/src/main/scala/akka/http/engine/ws/Handshake.scala b/akka-http-core/src/main/scala/akka/http/engine/ws/Handshake.scala
index e57d07ffde..b6113d7ef5 100644
--- a/akka-http-core/src/main/scala/akka/http/engine/ws/Handshake.scala
+++ b/akka-http-core/src/main/scala/akka/http/engine/ws/Handshake.scala
@@ -11,6 +11,7 @@ import akka.parboiled2.util.Base64
 import akka.stream.FlowMaterializer
 import akka.stream.scaladsl.Flow
 
+import scala.collection.immutable.Seq
 import scala.reflect.ClassTag
 
 /**
@@ -70,6 +71,7 @@ private[http] object Handshake {
     val version = find[`Sec-WebSocket-Version`]
     val origin = find[Origin]
     val protocol = find[`Sec-WebSocket-Protocol`]
+    val supportedProtocols = protocol.toList.flatMap(_.protocols)
     val extensions = find[`Sec-WebSocket-Extensions`]
 
     def isValidKey(key: String): Boolean = Base64.rfc2045().decode(key).length == 16
@@ -80,8 +82,13 @@ private[http] object Handshake {
       key.exists(k ⇒ isValidKey(k.key))) {
 
       val header = new UpgradeToWebsocketLowLevel {
-        def handleFrames(handlerFlow: Flow[FrameEvent, FrameEvent, Any])(implicit mat: FlowMaterializer): HttpResponse =
-          buildResponse(key.get, handlerFlow)
+        def requestedProtocols: Seq[String] = supportedProtocols
+
+        def handleFrames(handlerFlow: Flow[FrameEvent, FrameEvent, Any], subprotocol: Option[String])(implicit mat: FlowMaterializer): HttpResponse = {
+          require(subprotocol.forall(chosen ⇒ supportedProtocols.contains(chosen)),
+            s"Tried to choose invalid subprotocol '$subprotocol' which wasn't offered by the client: [${requestedProtocols.mkString(", ")}]")
+          buildResponse(key.get, handlerFlow, subprotocol)
+        }
       }
       Some(header)
     } else None
@@ -106,12 +113,13 @@ private[http] object Handshake {
         concatenated value to obtain a 20-byte value and base64-
         encoding (see Section 4 of [RFC4648]) this 20-byte hash.
    */
-  def buildResponse(key: `Sec-WebSocket-Key`, handlerFlow: Flow[FrameEvent, FrameEvent, Any])(implicit mat: FlowMaterializer): HttpResponse =
+  def buildResponse(key: `Sec-WebSocket-Key`, handlerFlow: Flow[FrameEvent, FrameEvent, Any], subprotocol: Option[String])(implicit mat: FlowMaterializer): HttpResponse =
     HttpResponse(
       StatusCodes.SwitchingProtocols,
-      List(
-        Upgrade(List(UpgradeProtocol("websocket"))),
-        Connection(List("upgrade")),
-        `Sec-WebSocket-Accept`.forKey(key),
-        UpgradeToWebsocketResponseHeader(handlerFlow)))
+      subprotocol.map(p ⇒ `Sec-WebSocket-Protocol`(Seq(p))).toList :::
+        List(
+          Upgrade(List(UpgradeProtocol("websocket"))),
+          Connection(List("upgrade")),
+          `Sec-WebSocket-Accept`.forKey(key),
+          UpgradeToWebsocketResponseHeader(handlerFlow)))
 }
diff --git a/akka-http-core/src/main/scala/akka/http/engine/ws/UpgradeToWebsocketLowLevel.scala b/akka-http-core/src/main/scala/akka/http/engine/ws/UpgradeToWebsocketLowLevel.scala
index 1c40e5d489..1408d41be6 100644
--- a/akka-http-core/src/main/scala/akka/http/engine/ws/UpgradeToWebsocketLowLevel.scala
+++ b/akka-http-core/src/main/scala/akka/http/engine/ws/UpgradeToWebsocketLowLevel.scala
@@ -25,8 +25,8 @@ private[http] abstract class UpgradeToWebsocketLowLevel extends InternalCustomHe
    *
    * INTERNAL API (for now)
    */
-  private[http] def handleFrames(handlerFlow: Flow[FrameEvent, FrameEvent, Any])(implicit mat: FlowMaterializer): HttpResponse
+  private[http] def handleFrames(handlerFlow: Flow[FrameEvent, FrameEvent, Any], subprotocol: Option[String] = None)(implicit mat: FlowMaterializer): HttpResponse
 
-  override def handleMessages(handlerFlow: Flow[Message, Message, Any])(implicit mat: FlowMaterializer): HttpResponse =
-    handleFrames(Websocket.handleMessages(handlerFlow))
+  override def handleMessages(handlerFlow: Flow[Message, Message, Any], subprotocol: Option[String] = None)(implicit mat: FlowMaterializer): HttpResponse =
+    handleFrames(Websocket.handleMessages(handlerFlow), subprotocol)
 }
diff --git a/akka-http-core/src/main/scala/akka/http/model/ws/UpgradeToWebsocket.scala b/akka-http-core/src/main/scala/akka/http/model/ws/UpgradeToWebsocket.scala
index c63b4ea2a4..7325d46835 100644
--- a/akka-http-core/src/main/scala/akka/http/model/ws/UpgradeToWebsocket.scala
+++ b/akka-http-core/src/main/scala/akka/http/model/ws/UpgradeToWebsocket.scala
@@ -4,6 +4,7 @@
 
 package akka.http.model.ws
 
+import scala.collection.immutable
 import akka.stream.FlowMaterializer
 import akka.stream.scaladsl.Flow
 
@@ -13,16 +14,22 @@ import akka.http.model.{ HttpHeader, HttpResponse }
  * A custom header that will be added to an Websocket upgrade HttpRequest that
  * enables a request handler to upgrade this connection to a Websocket connection and
  * registers a Websocket handler.
- *
- * FIXME: needs to be able to choose subprotocols as possibly agreed on in the websocket handshake
  */
 trait UpgradeToWebsocket extends HttpHeader {
+  /**
+   * A sequence of protocols the client accepts.
+   *
+   * See http://tools.ietf.org/html/rfc6455#section-1.9
+   */
+  def requestedProtocols: immutable.Seq[String]
+
   /**
    * The high-level interface to create a Websocket server based on "messages".
    *
    * Returns a response to return in a request handler that will signal the
    * low-level HTTP implementation to upgrade the connection to Websocket and
-   * use the supplied handler to handle incoming Websocket messages.
+   * use the supplied handler to handle incoming Websocket messages. Optionally,
+   * a subprotocol out of the ones requested by the client can be chosen.
    */
-  def handleMessages(handlerFlow: Flow[Message, Message, Any])(implicit mat: FlowMaterializer): HttpResponse
+  def handleMessages(handlerFlow: Flow[Message, Message, Any], subprotocol: Option[String] = None)(implicit mat: FlowMaterializer): HttpResponse
 }
diff --git a/akka-http-tests/src/test/scala/akka/http/server/directives/WebsocketDirectivesSpec.scala b/akka-http-tests/src/test/scala/akka/http/server/directives/WebsocketDirectivesSpec.scala
index 2de7c9ca95..e05c6ab17e 100644
--- a/akka-http-tests/src/test/scala/akka/http/server/directives/WebsocketDirectivesSpec.scala
+++ b/akka-http-tests/src/test/scala/akka/http/server/directives/WebsocketDirectivesSpec.scala
@@ -14,6 +14,8 @@ import akka.http.util.Rendering
 import akka.stream.FlowMaterializer
 import akka.stream.scaladsl.Flow
 
+import scala.collection.immutable.Seq
+
 class WebsocketDirectivesSpec extends RoutingSpec {
   "the handleWebsocketMessages directive" should {
     "handle websocket requests" in {
@@ -39,7 +41,9 @@ class WebsocketDirectivesSpec extends RoutingSpec {
     }
   def upgradeToWebsocketHeaderMock: UpgradeToWebsocket =
     new InternalCustomHeader("UpgradeToWebsocketMock") with UpgradeToWebsocket {
-      def handleMessages(handlerFlow: Flow[Message, Message, Any])(implicit mat: FlowMaterializer): HttpResponse =
+      def requestedProtocols: Seq[String] = Nil
+
+      def handleMessages(handlerFlow: Flow[Message, Message, Any], subprotocol: Option[String])(implicit mat: FlowMaterializer): HttpResponse =
         HttpResponse(StatusCodes.SwitchingProtocols)
     }
 }