diff --git a/src/internal/streams.cc b/src/internal/streams.cc
index b6ddaef..29b4f49 100644
--- a/src/internal/streams.cc
+++ b/src/internal/streams.cc
@@ -53,7 +53,7 @@ bool unpack_stereo_img_data(
   }
 
   std::uint8_t checksum = 0;
-  for (std::size_t i = 1, n = packet_n - 2; i <= n; i++) {
+  for (std::size_t i = 2, n = packet_n - 2; i <= n; i++) {  // content: [2,9]
     checksum = (checksum ^ packet[i]);
   }
   if (checksum != img_packet.checksum) {