diff --git a/akka-http-core/src/main/scala/akka/http/impl/engine/parsing/BodyPartParser.scala b/akka-http-core/src/main/scala/akka/http/impl/engine/parsing/BodyPartParser.scala
index 7086f937a9..36d874d90a 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/engine/parsing/BodyPartParser.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/engine/parsing/BodyPartParser.scala
@@ -260,9 +260,10 @@ private[http] object BodyPartParser {
   }
 
   sealed trait Output
-  final case class BodyPartStart(headers: List[HttpHeader], createEntity: Source[Output, Unit] ⇒ BodyPartEntity) extends Output
+  sealed trait PartStart extends Output
+  final case class BodyPartStart(headers: List[HttpHeader], createEntity: Source[Output, Unit] ⇒ BodyPartEntity) extends PartStart
   final case class EntityPart(data: ByteString) extends Output
-  final case class ParseError(info: ErrorInfo) extends Output
+  final case class ParseError(info: ErrorInfo) extends PartStart
 
   final case class Settings(
     maxHeaderNameLength: Int,
diff --git a/akka-http/src/main/scala/akka/http/scaladsl/unmarshalling/MultipartUnmarshallers.scala b/akka-http/src/main/scala/akka/http/scaladsl/unmarshalling/MultipartUnmarshallers.scala
index e5a6dfe317..802c758008 100644
--- a/akka-http/src/main/scala/akka/http/scaladsl/unmarshalling/MultipartUnmarshallers.scala
+++ b/akka-http/src/main/scala/akka/http/scaladsl/unmarshalling/MultipartUnmarshallers.scala
@@ -88,7 +88,7 @@ trait MultipartUnmarshallers {
                   case _ ⇒
                     val bodyParts = entity.dataBytes
                       .transform(() ⇒ parser)
-                      .splitWhen(_.isInstanceOf[BodyPartStart])
+                      .splitWhen(_.isInstanceOf[PartStart])
                       .via(headAndTailFlow)
                       .collect {
                         case (BodyPartStart(headers, createEntity), entityParts) ⇒ createBodyPart(createEntity(entityParts), headers)