diff --git a/packer/rpc/client.go b/packer/rpc/client.go
index 99f0b296d..4dd9deb47 100644
--- a/packer/rpc/client.go
+++ b/packer/rpc/client.go
@@ -15,14 +15,12 @@ type Client struct {
 }
 
 func NewClient(rwc io.ReadWriteCloser) (*Client, error) {
-	// Create the MuxConn around the RWC and get the client to server stream.
-	// This is the primary stream that we use to communicate with the
-	// remote RPC server. On the remote side Server.ServeConn also listens
-	// on this stream ID.
-	mux := NewMuxConn(rwc)
-	clientConn, err := mux.Dial(0)
+	return NewClientWithMux(NewMuxConn(rwc), 0)
+}
+
+func NewClientWithMux(mux *MuxConn, streamId uint32) (*Client, error) {
+	clientConn, err := mux.Dial(streamId)
 	if err != nil {
-		mux.Close()
 		return nil, err
 	}
 
@@ -37,7 +35,7 @@ func (c *Client) Close() error {
 		return err
 	}
 
-	return c.mux.Close()
+	return nil
 }
 
 func (c *Client) Artifact() packer.Artifact {
@@ -56,12 +54,13 @@ func (c *Client) Cache() packer.Cache {
 func (c *Client) PostProcessor() packer.PostProcessor {
 	return &postProcessor{
 		client: c.client,
+		mux:    c.mux,
 	}
 }
 
 func (c *Client) Ui() packer.Ui {
 	return &Ui{
-		client: c.client,
+		client:   c.client,
 		endpoint: DefaultUiEndpoint,
 	}
 }
diff --git a/packer/rpc/muxconn.go b/packer/rpc/muxconn.go
index 7247d4ed1..24e57fd63 100644
--- a/packer/rpc/muxconn.go
+++ b/packer/rpc/muxconn.go
@@ -21,7 +21,7 @@ type MuxConn struct {
 	curId   uint32
 	rwc     io.ReadWriteCloser
 	streams map[uint32]*Stream
-	mu      sync.RWMutex
+	mu      sync.Mutex
 	wlock   sync.Mutex
 }
 
diff --git a/packer/rpc/post_processor.go b/packer/rpc/post_processor.go
index 20e4f9b70..2a0dfe62a 100644
--- a/packer/rpc/post_processor.go
+++ b/packer/rpc/post_processor.go
@@ -9,14 +9,14 @@ import (
 // executed over an RPC connection.
 type postProcessor struct {
 	client *rpc.Client
-	server *rpc.Server
+	mux    *MuxConn
 }
 
 // PostProcessorServer wraps a packer.PostProcessor implementation and makes it
 // exportable as part of a Golang RPC server.
 type PostProcessorServer struct {
 	client *rpc.Client
-	server *rpc.Server
+	mux    *MuxConn
 	p      packer.PostProcessor
 }
 
@@ -24,15 +24,10 @@ type PostProcessorConfigureArgs struct {
 	Configs []interface{}
 }
 
-type PostProcessorPostProcessArgs struct {
-	ArtifactEndpoint string
-	UiEndpoint       string
-}
-
 type PostProcessorProcessResponse struct {
-	Err              error
-	Keep             bool
-	ArtifactEndpoint string
+	Err      error
+	Keep     bool
+	StreamId uint32
 }
 
 func PostProcessor(client *rpc.Client) *postProcessor {
@@ -49,21 +44,14 @@ func (p *postProcessor) Configure(raw ...interface{}) (err error) {
 }
 
 func (p *postProcessor) PostProcess(ui packer.Ui, a packer.Artifact) (packer.Artifact, bool, error) {
-	artifactEndpoint := registerComponent(p.server, "Artifact", &ArtifactServer{
-		artifact: a,
-	}, true)
-
-	uiEndpoint := registerComponent(p.server, "Ui", &UiServer{
-		ui: ui,
-	}, true)
-
-	args := PostProcessorPostProcessArgs{
-		ArtifactEndpoint: artifactEndpoint,
-		UiEndpoint:       uiEndpoint,
-	}
+	nextId := p.mux.NextId()
+	server := NewServerWithMux(p.mux, nextId)
+	server.RegisterArtifact(a)
+	server.RegisterUi(ui)
+	go server.Serve()
 
 	var response PostProcessorProcessResponse
-	if err := p.client.Call("PostProcessor.PostProcess", &args, &response); err != nil {
+	if err := p.client.Call("PostProcessor.PostProcess", nextId, &response); err != nil {
 		return nil, false, err
 	}
 
@@ -71,14 +59,16 @@ func (p *postProcessor) PostProcess(ui packer.Ui, a packer.Artifact) (packer.Art
 		return nil, false, response.Err
 	}
 
-	if response.ArtifactEndpoint == "" {
+	if response.StreamId == 0 {
 		return nil, false, nil
 	}
 
-	return &artifact{
-		client:   p.client,
-		endpoint: response.ArtifactEndpoint,
-	}, response.Keep, nil
+	client, err := NewClientWithMux(p.mux, response.StreamId)
+	if err != nil {
+		return nil, false, err
+	}
+
+	return client.Artifact(), response.Keep, nil
 }
 
 func (p *PostProcessorServer) Configure(args *PostProcessorConfigureArgs, reply *error) error {
@@ -90,23 +80,20 @@ func (p *PostProcessorServer) Configure(args *PostProcessorConfigureArgs, reply
 	return nil
 }
 
-func (p *PostProcessorServer) PostProcess(args *PostProcessorPostProcessArgs, reply *PostProcessorProcessResponse) error {
-	artifact := &artifact{
-		client:   p.client,
-		endpoint: args.ArtifactEndpoint,
+func (p *PostProcessorServer) PostProcess(streamId uint32, reply *PostProcessorProcessResponse) error {
+	client, err := NewClientWithMux(p.mux, streamId)
+	if err != nil {
+		return NewBasicError(err)
 	}
+	defer client.Close()
 
-	ui := &Ui{
-		client:   p.client,
-		endpoint: args.UiEndpoint,
-	}
-
-	var artifactEndpoint string
-	artifactResult, keep, err := p.p.PostProcess(ui, artifact)
+	streamId = 0
+	artifactResult, keep, err := p.p.PostProcess(client.Ui(), client.Artifact())
 	if err == nil && artifactResult != nil {
-		artifactEndpoint = registerComponent(p.server, "Artifact", &ArtifactServer{
-			artifact: artifactResult,
-		}, true)
+		streamId = p.mux.NextId()
+		server := NewServerWithMux(p.mux, streamId)
+		server.RegisterArtifact(artifactResult)
+		go server.Serve()
 	}
 
 	if err != nil {
@@ -114,9 +101,9 @@ func (p *PostProcessorServer) PostProcess(args *PostProcessorPostProcessArgs, re
 	}
 
 	*reply = PostProcessorProcessResponse{
-		Err:              err,
-		Keep:             keep,
-		ArtifactEndpoint: artifactEndpoint,
+		Err:      err,
+		Keep:     keep,
+		StreamId: streamId,
 	}
 
 	return nil
diff --git a/packer/rpc/post_processor_test.go b/packer/rpc/post_processor_test.go
index 418889ac5..d469ee4e0 100644
--- a/packer/rpc/post_processor_test.go
+++ b/packer/rpc/post_processor_test.go
@@ -13,6 +13,7 @@ type TestPostProcessor struct {
 	configVal    []interface{}
 	ppCalled     bool
 	ppArtifact   packer.Artifact
+	ppArtifactId string
 	ppUi         packer.Ui
 }
 
@@ -25,6 +26,7 @@ func (pp *TestPostProcessor) Configure(v ...interface{}) error {
 func (pp *TestPostProcessor) PostProcess(ui packer.Ui, a packer.Artifact) (packer.Artifact, bool, error) {
 	pp.ppCalled = true
 	pp.ppArtifact = a
+	pp.ppArtifactId = a.Id()
 	pp.ppUi = ui
 	return testPostProcessorArtifact, false, nil
 }
@@ -70,8 +72,8 @@ func TestPostProcessorRPC(t *testing.T) {
 		t.Fatal("postprocess should be called")
 	}
 
-	if p.ppArtifact.Id() != "ppTestId" {
-		t.Fatal("unknown artifact")
+	if p.ppArtifactId != "ppTestId" {
+		t.Fatalf("unknown artifact: %s", p.ppArtifact.Id())
 	}
 
 	if artifact.Id() != "id" {
diff --git a/packer/rpc/server_new.go b/packer/rpc/server_new.go
index afed8fe58..4f531f187 100644
--- a/packer/rpc/server_new.go
+++ b/packer/rpc/server_new.go
@@ -21,15 +21,21 @@ const (
 // Server represents an RPC server for Packer. This must be paired on
 // the other side with a Client.
 type Server struct {
-	mux    *MuxConn
-	server *rpc.Server
+	mux      *MuxConn
+	streamId uint32
+	server   *rpc.Server
 }
 
 // NewServer returns a new Packer RPC server.
 func NewServer(conn io.ReadWriteCloser) *Server {
+	return NewServerWithMux(NewMuxConn(conn), 0)
+}
+
+func NewServerWithMux(mux *MuxConn, streamId uint32) *Server {
 	return &Server{
-		mux:    NewMuxConn(conn),
-		server: rpc.NewServer(),
+		mux:      mux,
+		streamId: streamId,
+		server:   rpc.NewServer(),
 	}
 }
 
@@ -51,7 +57,8 @@ func (s *Server) RegisterCache(c packer.Cache) {
 
 func (s *Server) RegisterPostProcessor(p packer.PostProcessor) {
 	s.server.RegisterName(DefaultPostProcessorEndpoint, &PostProcessorServer{
-		p: p,
+		mux: s.mux,
+		p:   p,
 	})
 }
 
@@ -66,7 +73,7 @@ func (s *Server) RegisterUi(ui packer.Ui) {
 func (s *Server) Serve() {
 	// Accept a connection on stream ID 0, which is always used for
 	// normal client to server connections.
-	stream, err := s.mux.Accept(0)
+	stream, err := s.mux.Accept(s.streamId)
 	defer stream.Close()
 	if err != nil {
 		log.Printf("[ERR] Error retrieving stream for serving: %s", err)