diff --git a/packer/rpc/build.go b/packer/rpc/build.go
index 2df03a6ab..f2f7d48ab 100644
--- a/packer/rpc/build.go
+++ b/packer/rpc/build.go
@@ -107,7 +107,8 @@ func (b *BuildServer) Run(args *BuildRunArgs, reply *[]string) error {
 		return err
 	}
 
-	artifacts, err := b.build.Run(&Ui{client}, Cache(client))
+	ui := &Ui{client: client}
+	artifacts, err := b.build.Run(ui, Cache(client))
 	if err != nil {
 		return NewBasicError(err)
 	}
diff --git a/packer/rpc/builder.go b/packer/rpc/builder.go
index 42f92c4d4..0c5dfab37 100644
--- a/packer/rpc/builder.go
+++ b/packer/rpc/builder.go
@@ -146,7 +146,7 @@ func (b *BuilderServer) Run(args *BuilderRunArgs, reply *interface{}) error {
 
 		cache := Cache(client)
 		hook := Hook(client)
-		ui := &Ui{client}
+		ui := &Ui{client: client}
 		artifact, responseErr := b.builder.Run(ui, hook, cache)
 		responseAddress := ""
 
diff --git a/packer/rpc/environment.go b/packer/rpc/environment.go
index 36db72c56..aaf0db412 100644
--- a/packer/rpc/environment.go
+++ b/packer/rpc/environment.go
@@ -114,7 +114,7 @@ func (e *Environment) Ui() packer.Ui {
 		panic(err)
 	}
 
-	return &Ui{client}
+	return &Ui{client: client}
 }
 
 func (e *EnvironmentServer) Builder(name *string, reply *string) error {
diff --git a/packer/rpc/hook.go b/packer/rpc/hook.go
index 223b96df2..cede08302 100644
--- a/packer/rpc/hook.go
+++ b/packer/rpc/hook.go
@@ -51,7 +51,7 @@ func (h *HookServer) Run(args *HookRunArgs, reply *interface{}) error {
 		return err
 	}
 
-	if err := h.hook.Run(args.Name, &Ui{client}, Communicator(client), args.Data); err != nil {
+	if err := h.hook.Run(args.Name, &Ui{client: client}, Communicator(client), args.Data); err != nil {
 		return NewBasicError(err)
 	}
 
diff --git a/packer/rpc/post_processor.go b/packer/rpc/post_processor.go
index 0a5eaefd3..2f743eb65 100644
--- a/packer/rpc/post_processor.go
+++ b/packer/rpc/post_processor.go
@@ -82,7 +82,7 @@ func (p *PostProcessorServer) PostProcess(address string, reply *PostProcessorPr
 
 	responseAddress := ""
 
-	artifact, keep, err := p.p.PostProcess(&Ui{client}, Artifact(client))
+	artifact, keep, err := p.p.PostProcess(&Ui{client: client}, Artifact(client))
 	if err == nil && artifact != nil {
 		server := rpc.NewServer()
 		RegisterArtifact(server, artifact)
diff --git a/packer/rpc/provisioner.go b/packer/rpc/provisioner.go
index 4cd329d6b..a62f97d45 100644
--- a/packer/rpc/provisioner.go
+++ b/packer/rpc/provisioner.go
@@ -71,7 +71,7 @@ func (p *ProvisionerServer) Provision(args *ProvisionerProvisionArgs, reply *int
 	}
 
 	comm := Communicator(client)
-	ui := &Ui{client}
+	ui := &Ui{client: client}
 
 	if err := p.p.Provision(ui, comm); err != nil {
 		return NewBasicError(err)
diff --git a/packer/rpc/server.go b/packer/rpc/server.go
index f6098ea7a..c9154160a 100644
--- a/packer/rpc/server.go
+++ b/packer/rpc/server.go
@@ -1,73 +1,93 @@
 package rpc
 
 import (
+	"fmt"
 	"github.com/mitchellh/packer/packer"
 	"net/rpc"
+	"sync/atomic"
 )
 
+// This keeps track of the endpoint ID to use when registering artifacts.
+var endpointId uint64 = 0
+
 // Registers the appropriate endpoint on an RPC server to serve an
 // Artifact.
 func RegisterArtifact(s *rpc.Server, a packer.Artifact) {
-	s.RegisterName("Artifact", &ArtifactServer{a})
+	registerComponent(s, "Artifact", &ArtifactServer{a}, false)
 }
 
 // Registers the appropriate endpoint on an RPC server to serve a
 // Packer Build.
 func RegisterBuild(s *rpc.Server, b packer.Build) {
-	s.RegisterName("Build", &BuildServer{b})
+	registerComponent(s, "Build", &BuildServer{b}, false)
 }
 
 // Registers the appropriate endpoint on an RPC server to serve a
 // Packer Builder.
 func RegisterBuilder(s *rpc.Server, b packer.Builder) {
-	s.RegisterName("Builder", &BuilderServer{b})
+	registerComponent(s, "Builder", &BuilderServer{b}, false)
 }
 
 // Registers the appropriate endpoint on an RPC server to serve a
 // Packer Cache.
 func RegisterCache(s *rpc.Server, c packer.Cache) {
-	s.RegisterName("Cache", &CacheServer{c})
+	registerComponent(s, "Cache", &CacheServer{c}, false)
 }
 
 // Registers the appropriate endpoint on an RPC server to serve a
 // Packer Command.
 func RegisterCommand(s *rpc.Server, c packer.Command) {
-	s.RegisterName("Command", &CommandServer{c})
+	registerComponent(s, "Command", &CommandServer{c}, false)
 }
 
 // Registers the appropriate endpoint on an RPC server to serve a
 // Packer Communicator.
 func RegisterCommunicator(s *rpc.Server, c packer.Communicator) {
-	s.RegisterName("Communicator", &CommunicatorServer{c})
+	registerComponent(s, "Communicator", &CommunicatorServer{c}, false)
 }
 
 // Registers the appropriate endpoint on an RPC server to serve a
 // Packer Environment
 func RegisterEnvironment(s *rpc.Server, e packer.Environment) {
-	s.RegisterName("Environment", &EnvironmentServer{e})
+	registerComponent(s, "Environment", &EnvironmentServer{e}, false)
 }
 
 // Registers the appropriate endpoint on an RPC server to serve a
 // Hook.
-func RegisterHook(s *rpc.Server, hook packer.Hook) {
-	s.RegisterName("Hook", &HookServer{hook})
+func RegisterHook(s *rpc.Server, h packer.Hook) {
+	registerComponent(s, "Hook", &HookServer{h}, false)
 }
 
 // Registers the appropriate endpoing on an RPC server to serve a
 // PostProcessor.
 func RegisterPostProcessor(s *rpc.Server, p packer.PostProcessor) {
-	s.RegisterName("PostProcessor", &PostProcessorServer{p})
+	registerComponent(s, "PostProcessor", &PostProcessorServer{p}, false)
 }
 
 // Registers the appropriate endpoint on an RPC server to serve a packer.Provisioner
 func RegisterProvisioner(s *rpc.Server, p packer.Provisioner) {
-	s.RegisterName("Provisioner", &ProvisionerServer{p})
+	registerComponent(s, "Provisioner", &ProvisionerServer{p}, false)
 }
 
 // Registers the appropriate endpoint on an RPC server to serve a
 // Packer UI
 func RegisterUi(s *rpc.Server, ui packer.Ui) {
-	s.RegisterName("Ui", &UiServer{ui})
+	registerComponent(s, "Ui", &UiServer{ui}, false)
+}
+
+// registerComponent registers a single Packer RPC component onto
+// the RPC server. If id is true, then a unique ID number will be appended
+// onto the end of the endpoint.
+//
+// The endpoint name is returned.
+func registerComponent(s *rpc.Server, name string, rcvr interface{}, id bool) string {
+	endpoint := name
+	if id {
+		fmt.Sprintf("%s.%d", endpoint, atomic.AddUint64(&endpointId, 1))
+	}
+
+	s.RegisterName(endpoint, rcvr)
+	return endpoint
 }
 
 func serveSingleConn(s *rpc.Server) string {
diff --git a/packer/rpc/ui.go b/packer/rpc/ui.go
index 4d7ccc57f..1857e4928 100644
--- a/packer/rpc/ui.go
+++ b/packer/rpc/ui.go
@@ -9,7 +9,8 @@ import (
 // An implementation of packer.Ui where the Ui is actually executed
 // over an RPC connection.
 type Ui struct {
-	client *rpc.Client
+	client   *rpc.Client
+	endpoint string
 }
 
 // UiServer wraps a packer.Ui implementation and makes it exportable
@@ -25,12 +26,12 @@ type UiMachineArgs struct {
 }
 
 func (u *Ui) Ask(query string) (result string, err error) {
-	err = u.client.Call("Ui.Ask", query, &result)
+	err = u.client.Call(u.endpoint+".Ask", query, &result)
 	return
 }
 
 func (u *Ui) Error(message string) {
-	if err := u.client.Call("Ui.Error", message, new(interface{})); err != nil {
+	if err := u.client.Call(u.endpoint+".Error", message, new(interface{})); err != nil {
 		log.Printf("Error in Ui RPC call: %s", err)
 	}
 }
@@ -41,19 +42,19 @@ func (u *Ui) Machine(t string, args ...string) {
 		Args:     args,
 	}
 
-	if err := u.client.Call("Ui.Machine", rpcArgs, new(interface{})); err != nil {
+	if err := u.client.Call(u.endpoint+".Machine", rpcArgs, new(interface{})); err != nil {
 		log.Printf("Error in Ui RPC call: %s", err)
 	}
 }
 
 func (u *Ui) Message(message string) {
-	if err := u.client.Call("Ui.Message", message, new(interface{})); err != nil {
+	if err := u.client.Call(u.endpoint+".Message", message, new(interface{})); err != nil {
 		log.Printf("Error in Ui RPC call: %s", err)
 	}
 }
 
 func (u *Ui) Say(message string) {
-	if err := u.client.Call("Ui.Say", message, new(interface{})); err != nil {
+	if err := u.client.Call(u.endpoint+".Say", message, new(interface{})); err != nil {
 		log.Printf("Error in Ui RPC call: %s", err)
 	}
 }
diff --git a/packer/rpc/ui_test.go b/packer/rpc/ui_test.go
index 8a85c5573..3a46bf02c 100644
--- a/packer/rpc/ui_test.go
+++ b/packer/rpc/ui_test.go
@@ -62,7 +62,7 @@ func TestUiRPC(t *testing.T) {
 		panic(err)
 	}
 
-	uiClient := &Ui{client}
+	uiClient := &Ui{client: client, endpoint: "Ui"}
 
 	// Basic error and say tests
 	result, err := uiClient.Ask("query")