diff --git a/codecs/vp9_packet.go b/codecs/vp9_packet.go
index 0396554..9d05340 100644
--- a/codecs/vp9_packet.go
+++ b/codecs/vp9_packet.go
@@ -25,12 +25,12 @@ const (
 // Payload fragments an VP9 packet across one or more byte arrays
 func (p *VP9Payloader) Payload(mtu int, payload []byte) [][]byte {
 	/*
-	 * https://www.ietf.org/id/draft-ietf-payload-vp9-10.txt
+	 * https://www.ietf.org/id/draft-ietf-payload-vp9-13.txt
 	 *
 	 * Flexible mode (F=1)
 	 *        0 1 2 3 4 5 6 7
 	 *       +-+-+-+-+-+-+-+-+
-	 *       |I|P|L|F|B|E|V|-| (REQUIRED)
+	 *       |I|P|L|F|B|E|V|Z| (REQUIRED)
 	 *       +-+-+-+-+-+-+-+-+
 	 *  I:   |M| PICTURE ID  | (REQUIRED)
 	 *       +-+-+-+-+-+-+-+-+
@@ -47,7 +47,7 @@ func (p *VP9Payloader) Payload(mtu int, payload []byte) [][]byte {
 	 * Non-flexible mode (F=0)
 	 *        0 1 2 3 4 5 6 7
 	 *       +-+-+-+-+-+-+-+-+
-	 *       |I|P|L|F|B|E|V|-| (REQUIRED)
+	 *       |I|P|L|F|B|E|V|Z| (REQUIRED)
 	 *       +-+-+-+-+-+-+-+-+
 	 *  I:   |M| PICTURE ID  | (RECOMMENDED)
 	 *       +-+-+-+-+-+-+-+-+
@@ -121,6 +121,7 @@ type VP9Packet struct {
 	B bool // Start of a frame
 	E bool // End of a frame
 	V bool // Scalability structure (SS) data present
+	Z bool // Not a reference frame for upper spatial layers
 
 	// Recommended headers
 	PictureID uint16 // 7 or 16 bits, picture ID
@@ -171,6 +172,7 @@ func (p *VP9Packet) Unmarshal(packet []byte) ([]byte, error) {
 	p.B = packet[0]&0x08 != 0
 	p.E = packet[0]&0x04 != 0
 	p.V = packet[0]&0x02 != 0
+	p.Z = packet[0]&0x01 != 0
 
 	pos := 1
 	var err error