diff --git a/codec/h265/lex.go b/codec/h265/lex.go
index 7baaf734..61a4dab7 100644
--- a/codec/h265/lex.go
+++ b/codec/h265/lex.go
@@ -83,6 +83,7 @@ func (l *Lexer) Lex(dst io.Writer, src io.Reader, delay time.Duration) error {
 		// If not currently fragmented then we ignore current write
 		if l.fragmented && nalType != typeFragmentation {
 			l.off = 0
+			l.fragmented = false
 			continue
 		}
 
@@ -137,7 +138,25 @@ func (l *Lexer) handleAggregation(d []byte) {
 // handleFragmentation parses NAL units from fragmentation packets and writes
 // them to the Lexer's buf.
 func (l *Lexer) handleFragmentation(d []byte) {
+	_d := d[3:]
+	if l.UsingDON {
+		_d = d[5:]
+	}
 
+	s := d[2]&0x80 == 1
+	e := d[2]&0x40 == 1
+	switch {
+	case s && !e:
+		l.fragmented = true
+		l.write(_d)
+	case !s && e:
+		l.fragmented = false
+		fallthrough
+	case !s && !e:
+		l.writeNoPrefix(_d)
+	default:
+		panic("bad fragmentation unit")
+	}
 }
 
 // handlePACI will handl PACI packets
@@ -147,11 +166,18 @@ func (l *Lexer) handlePACI(d []byte) {
 	panic("unsupported nal type")
 }
 
-// write writes a NAL unit to the Lexers buf in byte stream format using the
+// write writes a NAL unit to the Lexer's buf in byte stream format using the
 // start code.
 func (l *Lexer) write(d []byte) {
-	const startCode = "\x00\x00\x00\x01"
-	copy(l.buf[l.off:], []byte(startCode))
+	const prefix = "\x00\x00\x00\x01"
+	copy(l.buf[l.off:], []byte(prefix))
 	copy(l.buf[l.off+4:], d)
 	l.off += len(d) + 4
 }
+
+// writeNoPrefix writes data to the Lexer's buf. This is used for non start
+// fragmentations of a NALU.
+func (l *Lexer) writeNoPrefix(d []byte) {
+	copy(l.buf[l.off:], d)
+	l.off += len(d)
+}