diff --git a/book/source/glossary.md b/book/source/glossary.md
index 58900f2..f87bd6c 100644
--- a/book/source/glossary.md
+++ b/book/source/glossary.md
@@ -242,7 +242,7 @@ Inline Signature
     A {term}`Data Signature` which exists encapsulated alongside the data it was created for in an OpenPGP container. See [](forms-of-data-signatures).
 
 Issuer
-    An entity, that created an {term}`OpenPGP Signature Packet` using an {term}`Transferable Secret Key`.
+    An entity, that created an {term}`OpenPGP Signature Packet` using a {term}`Transferable Secret Key`.
 
 Issuer Fingerprint Subpacket
     A {term}`Subpacket` specifying the {term}`Fingerprint` of an {term}`Issuer Key`.