diff --git a/src/packet_format.md b/src/packet_format.md
index 9ba91f8..c0ec60d 100644
--- a/src/packet_format.md
+++ b/src/packet_format.md
@@ -8,5 +8,5 @@ All tapir packets are fixed length (8192 bytes) with the first 2 bytes indicated
 Once encrypted, the entire 8192 byte data packet is encrypted using [libsodium secretbox](https://libsodium.gitbook.io/doc/secret-key_cryptography/secretbox) using the standard structure (
 note in this case the actual usable size of the data packet is 8190-14 to accommodate the nonce included by secret box)
 
-For information on how th secret key is derived see the [authentication protocol](./authentication_protocol.md)
+For information on how the secret key is derived see the [authentication protocol](./authentication_protocol.md)