diff --git a/http2/configure_transport.go b/http2/configure_transport.go
index d87ba0f..4f720f5 100644
--- a/http2/configure_transport.go
+++ b/http2/configure_transport.go
@@ -32,7 +32,7 @@
 		t1.TLSClientConfig.NextProtos = append(t1.TLSClientConfig.NextProtos, "http/1.1")
 	}
 	upgradeFn := func(authority string, c *tls.Conn) http.RoundTripper {
-		addr := authorityAddr(authority)
+		addr := authorityAddr("https", authority)
 		if used, err := connPool.addConnIfNeeded(addr, t2, c); err != nil {
 			go c.Close()
 			return erringRoundTripper{err}
diff --git a/http2/transport.go b/http2/transport.go
index 2ae7437..b42eae7 100644
--- a/http2/transport.go
+++ b/http2/transport.go
@@ -77,6 +77,10 @@
 	// uncompressed.
 	DisableCompression bool
 
+	// AllowHTTP, if true, permits HTTP/2 requests using the insecure,
+	// plain-text "http" scheme. Note that this does not enable h2c support.
+	AllowHTTP bool
+
 	// MaxHeaderListSize is the http2 SETTINGS_MAX_HEADER_LIST_SIZE to
 	// send in the initial settings frame. It is how many bytes
 	// of response headers are allow. Unlike the http2 spec, zero here
@@ -275,20 +279,24 @@
 
 // authorityAddr returns a given authority (a host/IP, or host:port / ip:port)
 // and returns a host:port. The port 443 is added if needed.
-func authorityAddr(authority string) (addr string) {
+func authorityAddr(scheme string, authority string) (addr string) {
 	if _, _, err := net.SplitHostPort(authority); err == nil {
 		return authority
 	}
-	return net.JoinHostPort(authority, "443")
+	port := "443"
+	if scheme == "http" {
+		port = "80"
+	}
+	return net.JoinHostPort(authority, port)
 }
 
 // RoundTripOpt is like RoundTrip, but takes options.
 func (t *Transport) RoundTripOpt(req *http.Request, opt RoundTripOpt) (*http.Response, error) {
-	if req.URL.Scheme != "https" {
+	if !(req.URL.Scheme == "https" || (req.URL.Scheme == "http" && t.AllowHTTP)) {
 		return nil, errors.New("http2: unsupported scheme")
 	}
 
-	addr := authorityAddr(req.URL.Host)
+	addr := authorityAddr(req.URL.Scheme, req.URL.Host)
 	for {
 		cc, err := t.connPool().GetClientConn(req, addr)
 		if err != nil {
diff --git a/http2/transport_test.go b/http2/transport_test.go
index 7bba6a7..62c7ab1 100644
--- a/http2/transport_test.go
+++ b/http2/transport_test.go
@@ -53,6 +53,51 @@
 	res.Write(os.Stdout)
 }
 
+func startH2cServer(t *testing.T) net.Listener {
+	h2Server := &Server{}
+	l := newLocalListener(t)
+	go func() {
+		conn, err := l.Accept()
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		h2Server.ServeConn(conn, &ServeConnOpts{Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			fmt.Fprintf(w, "Hello, %v", r.URL.Path)
+		})})
+	}()
+	return l
+}
+
+func TestTransportH2c(t *testing.T) {
+	l := startH2cServer(t)
+	defer l.Close()
+	req, err := http.NewRequest("GET", "http://"+l.Addr().String()+"/foobar", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	tr := &Transport{
+		AllowHTTP: true,
+		DialTLS: func(network, addr string, cfg *tls.Config) (net.Conn, error) {
+			return net.Dial(network, addr)
+		},
+	}
+	res, err := tr.RoundTrip(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.ProtoMajor != 2 {
+		t.Fatal("proto not h2c")
+	}
+	body, err := ioutil.ReadAll(res.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got, want := string(body), "Hello, /foobar"; got != want {
+		t.Fatalf("response got %v, want %v", got, want)
+	}
+}
+
 func TestTransport(t *testing.T) {
 	const body = "sup"
 	st := newServerTester(t, func(w http.ResponseWriter, r *http.Request) {