diff --git a/codec/h265/lex_test.go b/codec/h265/lex_test.go
index 67ba22cf..e68d1833 100644
--- a/codec/h265/lex_test.go
+++ b/codec/h265/lex_test.go
@@ -44,9 +44,9 @@ func (r *rtpReader) Read(p []byte) (int, error) {
 		return 0, io.EOF
 	}
 	b := r.packets[r.idx]
-	copy(p, b)
+	n := copy(p, b)
 	r.idx++
-	return len(b), nil
+	return n, nil
 }
 
 // destination holds the access units extracted during the lexing process.