diff --git a/controller_test.go b/controller_test.go
index 63a2754..7b515a3 100644
--- a/controller_test.go
+++ b/controller_test.go
@@ -699,7 +699,7 @@ func (s *controllerSuite) TestAddFileReader(c *gc.C) {
 var versionResponse = `{"version": "unknown", "subversion": "", "capabilities": ["networks-management", "static-ipaddresses", "ipv6-deployment-ubuntu", "devices-management", "storage-deployment-ubuntu", "network-deployment-ubuntu"]}`
 
 type cleanup interface {
-	AddCleanup(testing.CleanupFunc)
+	AddCleanup(func(*gc.C))
 }
 
 // createTestServerController creates a controller backed on to a test server
diff --git a/dependencies.tsv b/dependencies.tsv
index 12fcacb..6312ca3 100644
--- a/dependencies.tsv
+++ b/dependencies.tsv
@@ -1,9 +1,9 @@
 github.com/juju/errors	git	1b5e39b83d1835fa480e0c2ddefb040ee82d58b3	2015-09-16T12:56:42Z
 github.com/juju/loggo	git	8477fc936adf0e382d680310047ca27e128a309a	2015-05-27T03:58:39Z
-github.com/juju/names	git	ef19de31613af3735aa69ba3b40accce2faf7316	2016-03-01T22:07:10Z
+github.com/juju/names	git	8a0aa0963bbacdc790914892e9ff942e94d6f795	2016-03-30T15:05:33Z
 github.com/juju/schema	git	1e25943f8c6fd6815282d6f1ac87091d21e14e19	2016-03-01T11:16:46Z
-github.com/juju/testing	git	45f216f8ef2a6fbed3f38cbcd57f68741d295053	2016-03-17T08:39:30Z
-github.com/juju/utils	git	af32cfaf28093965fdf63373d8447c489efb2875	2016-03-09T18:28:39Z
+github.com/juju/testing	git	162fafccebf20a4207ab93d63b986c230e3f4d2e	2016-04-04T09:43:17Z
+github.com/juju/utils	git	eb6cb958762135bb61aed1e0951f657c674d427f	2016-04-11T02:40:59Z
 github.com/juju/version	git	ef897ad7f130870348ce306f61332f5335355063	2015-11-27T20:34:00Z
 golang.org/x/crypto	git	aedad9a179ec1ea11b7064c57cbc6dc30d7724ec	2015-08-30T18:06:42Z
 gopkg.in/check.v1	git	4f90aeace3a26ad7021961c297b22c42160c7b25	2016-01-05T16:49:36Z
diff --git a/machine.go b/machine.go
index 0019ca3..83eaea8 100644
--- a/machine.go
+++ b/machine.go
@@ -4,7 +4,6 @@
 package gomaasapi
 
 import (
-	"encoding/base64"
 	"net/http"
 
 	"github.com/juju/errors"
@@ -174,7 +173,8 @@ func (m *machine) Devices(args DevicesArgs) ([]Device, error) {
 // StartArgs is an argument struct for passing parameters to the Machine.Start
 // method.
 type StartArgs struct {
-	UserData     []byte
+	// UserData needs to be Base64 encoded user data for cloud-init.
+	UserData     string
 	DistroSeries string
 	Kernel       string
 	Comment      string
@@ -182,12 +182,8 @@ type StartArgs struct {
 
 // Start implements Machine.
 func (m *machine) Start(args StartArgs) error {
-	var encodedUserData string
-	if args.UserData != nil {
-		encodedUserData = base64.StdEncoding.EncodeToString(args.UserData)
-	}
 	params := NewURLParams()
-	params.MaybeAdd("user_data", encodedUserData)
+	params.MaybeAdd("user_data", args.UserData)
 	params.MaybeAdd("distro_series", args.DistroSeries)
 	params.MaybeAdd("hwe_kernel", args.Kernel)
 	params.MaybeAdd("comment", args.Comment)
diff --git a/machine_test.go b/machine_test.go
index f973e84..c5e3821 100644
--- a/machine_test.go
+++ b/machine_test.go
@@ -4,7 +4,6 @@
 package gomaasapi
 
 import (
-	"encoding/base64"
 	"net/http"
 
 	"github.com/juju/errors"
@@ -100,7 +99,7 @@ func (s *machineSuite) TestStart(c *gc.C) {
 	server.AddPostResponse(machine.resourceURI+"?op=deploy", http.StatusOK, response)
 
 	err := machine.Start(StartArgs{
-		UserData:     []byte("userdata"),
+		UserData:     "userdata",
 		DistroSeries: "trusty",
 		Kernel:       "kernel",
 		Comment:      "a comment",
@@ -111,12 +110,12 @@ func (s *machineSuite) TestStart(c *gc.C) {
 
 	request := server.LastRequest()
 	// There should be one entry in the form values for each of the args.
-	c.Assert(request.PostForm, gc.HasLen, 4)
-	// The userdata should be base64 encoded.
-	userdata := request.PostForm.Get("user_data")
-	value, err := base64.StdEncoding.DecodeString(userdata)
-	c.Assert(err, jc.ErrorIsNil)
-	c.Assert(string(value), gc.Equals, "userdata")
+	form := request.PostForm
+	c.Assert(form, gc.HasLen, 4)
+	c.Check(form.Get("user_data"), gc.Equals, "userdata")
+	c.Check(form.Get("distro_series"), gc.Equals, "trusty")
+	c.Check(form.Get("hwe_kernel"), gc.Equals, "kernel")
+	c.Check(form.Get("comment"), gc.Equals, "a comment")
 }
 
 func (s *machineSuite) TestStartMachineNotFound(c *gc.C) {