diff --git a/book/cover.png b/book/cover.png
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diff --git a/book/index.adoc b/book/index.adoc
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+++ b/book/index.adoc
@@ -6,7 +6,7 @@
 :description: How to use Nix as a PHP Developer.
 :doctype: book
 :email: oliver@oliverdavies.uk
-// :front-cover-image: image:cover.png[width=1024,height=1024]
+:front-cover-image: image:cover.png[fit=fill]
 :icons: font
 :keywords: php software-development nix linux
 :leveloffset: +1