diff --git a/common/download.go b/common/download.go
index 2a0b37ee7..b5798b76c 100644
--- a/common/download.go
+++ b/common/download.go
@@ -43,6 +43,10 @@ type DownloadConfig struct {
 	// for the downloader will be used to verify with this checksum after
 	// it is downloaded.
 	Checksum []byte
+
+	// What to use for the user agent for HTTP requests. If set to "", use the
+	// default user agent provided by Go.
+	UserAgent string
 }
 
 // A DownloadClient helps download, verify checksums, etc.
@@ -73,8 +77,8 @@ func HashForType(t string) hash.Hash {
 func NewDownloadClient(c *DownloadConfig) *DownloadClient {
 	if c.DownloaderMap == nil {
 		c.DownloaderMap = map[string]Downloader{
-			"http":  new(HTTPDownloader),
-			"https": new(HTTPDownloader),
+			"http":  &HTTPDownloader{userAgent: c.UserAgent},
+			"https": &HTTPDownloader{userAgent: c.UserAgent},
 		}
 	}
 
@@ -182,8 +186,9 @@ func (d *DownloadClient) VerifyChecksum(path string) (bool, error) {
 // HTTPDownloader is an implementation of Downloader that downloads
 // files over HTTP.
 type HTTPDownloader struct {
-	progress uint
-	total    uint
+	progress  uint
+	total     uint
+	userAgent string
 }
 
 func (*HTTPDownloader) Cancel() {
@@ -197,6 +202,10 @@ func (d *HTTPDownloader) Download(dst io.Writer, src *url.URL) error {
 		return err
 	}
 
+	if d.userAgent != "" {
+		req.Header.Set("User-Agent", d.userAgent)
+	}
+
 	httpClient := &http.Client{
 		Transport: &http.Transport{
 			Proxy: http.ProxyFromEnvironment,
diff --git a/common/download_test.go b/common/download_test.go
index f1fec941e..57b4ba7bc 100644
--- a/common/download_test.go
+++ b/common/download_test.go
@@ -4,6 +4,8 @@ import (
 	"crypto/md5"
 	"encoding/hex"
 	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
 	"os"
 	"testing"
 )
@@ -41,6 +43,91 @@ func TestDownloadClient_VerifyChecksum(t *testing.T) {
 	}
 }
 
+func TestDownloadClientUsesDefaultUserAgent(t *testing.T) {
+	tf, err := ioutil.TempFile("", "packer")
+	if err != nil {
+		t.Fatalf("tempfile error: %s", err)
+	}
+	defer os.Remove(tf.Name())
+
+	defaultUserAgent := ""
+	asserted := false
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if defaultUserAgent == "" {
+			defaultUserAgent = r.UserAgent()
+		} else {
+			incomingUserAgent := r.UserAgent()
+			if incomingUserAgent != defaultUserAgent {
+				t.Fatalf("Expected user agent %s, got: %s", defaultUserAgent, incomingUserAgent)
+			}
+
+			asserted = true
+		}
+	}))
+
+	req, err := http.NewRequest("GET", server.URL, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	httpClient := &http.Client{
+		Transport: &http.Transport{
+			Proxy: http.ProxyFromEnvironment,
+		},
+	}
+
+	_, err = httpClient.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	config := &DownloadConfig{
+		Url:        server.URL,
+		TargetPath: tf.Name(),
+	}
+
+	client := NewDownloadClient(config)
+	_, err = client.Get()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !asserted {
+		t.Fatal("User-Agent never observed")
+	}
+}
+
+func TestDownloadClientSetsUserAgent(t *testing.T) {
+	tf, err := ioutil.TempFile("", "packer")
+	if err != nil {
+		t.Fatalf("tempfile error: %s", err)
+	}
+	defer os.Remove(tf.Name())
+
+	asserted := false
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		asserted = true
+		if r.UserAgent() != "fancy user agent" {
+			t.Fatalf("Expected useragent fancy user agent, got: %s", r.UserAgent())
+		}
+	}))
+	config := &DownloadConfig{
+		Url:        server.URL,
+		TargetPath: tf.Name(),
+		UserAgent:  "fancy user agent",
+	}
+
+	client := NewDownloadClient(config)
+	_, err = client.Get()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !asserted {
+		t.Fatal("HTTP request never made")
+	}
+}
+
 func TestHashForType(t *testing.T) {
 	if h := HashForType("md5"); h == nil {
 		t.Fatalf("md5 hash is nil")