diff --git a/codec/h264/lex.go b/codec/h264/lex.go
index e9cbe67c..81eca759 100644
--- a/codec/h264/lex.go
+++ b/codec/h264/lex.go
@@ -40,7 +40,7 @@ import (
 	"bitbucket.org/ausocean/av/protocol/rtp"
 )
 
-// NAL types.
+// NAL types (from https://tools.ietf.org/html/rfc6184#page-13)
 const (
 	// Single nal units bounds.
 	typeSingleNALULowBound  = 1