diff --git a/src/net/http/transport.go b/src/net/http/transport.go
index 41df906cf2..baf71d5e85 100644
--- a/src/net/http/transport.go
+++ b/src/net/http/transport.go
@@ -163,6 +163,22 @@ func (t *Transport) onceSetNextProtoDefaults() {
 		return
 	}
 	if t.TLSNextProto != nil {
+		// This is the documented way to disable http2 on a
+		// Transport.
+		return
+	}
+	if t.TLSClientConfig != nil {
+		// Be conservative for now (for Go 1.6) at least and
+		// don't automatically enable http2 if they've
+		// specified a custom TLS config. Let them opt-in
+		// themselves via http2.ConfigureTransport so we don't
+		// surprise them by modifying their tls.Config.
+		// Issue 14275.
+		return
+	}
+	if t.ExpectContinueTimeout != 0 {
+		// Unsupported in http2, so disable http2 for now.
+		// Issue 13851.
 		return
 	}
 	t2, err := http2configureTransport(t)
diff --git a/src/net/http/transport_test.go b/src/net/http/transport_test.go
index 8cb89a4220..0c901b30a4 100644
--- a/src/net/http/transport_test.go
+++ b/src/net/http/transport_test.go
@@ -2885,23 +2885,34 @@ func TestTransportPrefersResponseOverWriteError(t *testing.T) {
 }
 
 func TestTransportAutomaticHTTP2(t *testing.T) {
-	tr := &Transport{}
+	testTransportAutoHTTP(t, &Transport{}, true)
+}
+
+func TestTransportAutomaticHTTP2_TLSNextProto(t *testing.T) {
+	testTransportAutoHTTP(t, &Transport{
+		TLSNextProto: make(map[string]func(string, *tls.Conn) RoundTripper),
+	}, false)
+}
+
+func TestTransportAutomaticHTTP2_TLSConfig(t *testing.T) {
+	testTransportAutoHTTP(t, &Transport{
+		TLSClientConfig: new(tls.Config),
+	}, false)
+}
+
+func TestTransportAutomaticHTTP2_ExpectContinueTimeout(t *testing.T) {
+	testTransportAutoHTTP(t, &Transport{
+		ExpectContinueTimeout: 1 * time.Second,
+	}, false)
+}
+
+func testTransportAutoHTTP(t *testing.T, tr *Transport, wantH2 bool) {
 	_, err := tr.RoundTrip(new(Request))
 	if err == nil {
 		t.Error("expected error from RoundTrip")
 	}
-	if tr.TLSNextProto["h2"] == nil {
-		t.Errorf("HTTP/2 not registered.")
-	}
-
-	// Now with TLSNextProto set:
-	tr = &Transport{TLSNextProto: make(map[string]func(string, *tls.Conn) RoundTripper)}
-	_, err = tr.RoundTrip(new(Request))
-	if err == nil {
-		t.Error("expected error from RoundTrip")
-	}
-	if tr.TLSNextProto["h2"] != nil {
-		t.Errorf("HTTP/2 registered, despite non-nil TLSNextProto field")
+	if reg := tr.TLSNextProto["h2"] != nil; reg != wantH2 {
+		t.Errorf("HTTP/2 registered = %v; want %v", reg, wantH2)
 	}
 }