diff --git a/book/source/10-encryption.md b/book/source/10-encryption.md
index cdde41e..e3ce2b6 100644
--- a/book/source/10-encryption.md
+++ b/book/source/10-encryption.md
@@ -51,7 +51,7 @@ The typical combination of mechanisms for encryption in OpenPGP is a [hybrid cry
 
 ## Encapsulating session keys: PKESK, SKESK
 
-"*ESK" (encrypted session-key) is a family of mechanisms for encapsulation of symmetric key material. It has two branches:
+"*ESK" (encrypted session-key) packets are a family of mechanisms for encapsulation of symmetric key material. There are two branches:
 
 - [PKESK](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-public-key-encrypted-sessio): Uses asymmetric OpenPGP key material to protect a session key, and
 - [SKESK](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-symmetric-key-encrypted-ses): Uses passphrases to protect the symmetric key material, instead of OpenPGP asymmetric key material (this is less commonly used).