diff --git a/book/source/17-zoom_certificates.md b/book/source/17-zoom_certificates.md
index 6ce27be..65051b9 100644
--- a/book/source/17-zoom_certificates.md
+++ b/book/source/17-zoom_certificates.md
@@ -6,7 +6,7 @@ SPDX-License-Identifier: CC-BY-SA-4.0
 (zoom_certificates)=
 # Zooming in: Packet structure of certificates
 
-Now that we've established the concepts and  components that make up OpenPGP certificates , let's look at the internal details of an example certificate.
+Now that we've established the concepts and components that make up OpenPGP certificates , let's look at the internal details of an example certificate.
 
 ## A very minimal OpenPGP certificate