diff --git a/rtmp/packet.go b/rtmp/packet.go
index 79bd99fe..6d33731c 100644
--- a/rtmp/packet.go
+++ b/rtmp/packet.go
@@ -68,8 +68,12 @@ const (
 	RTMP_CHANNEL_SOURCE     = 0x04
 )
 
-// packetSize defines valid packet sizes.
-var packetSize = [...]int{12, 8, 4, 1}
+// headerSizes defines header sizes for header types 0, 1, 2 and 3 respectively:
+//   0: full header (12 bytes)
+//   1: header without message ID (8 bytes)
+//   2: basic header + timestamp (4 byes)
+//   3: basic header (chunk type and stream ID) (1 byte)
+var headerSizes = [...]int{12, 8, 4, 1}
 
 // packet defines an RTMP packet.
 type packet struct {
@@ -154,7 +158,7 @@ func readPacket(s *Session, pkt *packet) error {
 		s.channelsAllocatedIn = n
 	}
 
-	size := packetSize[pkt.headerType]
+	size := headerSizes[pkt.headerType]
 	switch {
 	case size == RTMP_LARGE_HEADER_SIZE:
 		pkt.hasAbsTimestamp = true
@@ -308,7 +312,7 @@ func sendPacket(s *Session, pkt *packet, queue bool) error {
 	if pkt.body != nil {
 		// Span from -packetsize for the type to the start of the body.
 		headBytes = pkt.header
-		origIdx = RTMP_MAX_HEADER_SIZE - packetSize[pkt.headerType]
+		origIdx = RTMP_MAX_HEADER_SIZE - headerSizes[pkt.headerType]
 	} else {
 		// Allocate a new header and allow 6 bytes of movement backward.
 		var hbuf [RTMP_MAX_HEADER_SIZE]byte
@@ -324,7 +328,7 @@ func sendPacket(s *Session, pkt *packet, queue bool) error {
 		cSize = 1
 	}
 
-	hSize := packetSize[pkt.headerType]
+	hSize := headerSizes[pkt.headerType]
 	if cSize != 0 {
 		origIdx -= cSize
 		hSize += cSize
@@ -365,7 +369,7 @@ func sendPacket(s *Session, pkt *packet, queue bool) error {
 		}
 	}
 
-	if packetSize[pkt.headerType] > 1 {
+	if headerSizes[pkt.headerType] > 1 {
 		res := ts
 		if ts > 0xffffff {
 			res = 0xffffff
@@ -374,14 +378,14 @@ func sendPacket(s *Session, pkt *packet, queue bool) error {
 		headerIdx += 3 // 24bits
 	}
 
-	if packetSize[pkt.headerType] > 4 {
+	if headerSizes[pkt.headerType] > 4 {
 		C_AMF_EncodeInt24(headBytes[headerIdx:], int32(pkt.bodySize))
 		headerIdx += 3 // 24bits
 		headBytes[headerIdx] = pkt.packetType
 		headerIdx++
 	}
 
-	if packetSize[pkt.headerType] > 8 {
+	if headerSizes[pkt.headerType] > 8 {
 		n := int(encodeInt32LE(headBytes[headerIdx:headerIdx+4], pkt.info))
 		headerIdx += n
 	}