diff --git a/book/source/adv/certificates.md b/book/source/adv/certificates.md
index 135baa2..2762235 100644
--- a/book/source/adv/certificates.md
+++ b/book/source/adv/certificates.md
@@ -190,14 +190,14 @@ Overall, certificate minimization for email presents a promising approach to enh
 
 [^space-example]: This example demonstrates how to minimize a certificate using GnuPG commands, targeting only relevant components:
 
-```sh
-gpg --export-options export-minimal,export-clean,no-export-attributes \
-    --export-filter keep-uid=mbox=wiktor@metacode.biz \
-    --export-filter 'drop-subkey=expired -t || revoked -t || usage =~ a' \
-    --export wiktor@metacode.biz
-```
-The process significantly reduces the certificate size from 152,322 bytes to just 3,771 bytes, demonstrating a substantial decrease in size by over 40 times. Such minimization is particularly crucial in contexts with strict size limitations, like embedding certificate data in email headers.
+    ```sh
+    gpg --export-options export-minimal,export-clean,no-export-attributes \
+        --export-filter keep-uid=mbox=wiktor@metacode.biz \
+        --export-filter 'drop-subkey=expired -t || revoked -t || usage =~ a' \
+        --export wiktor@metacode.biz
+    ```
 
+    The process significantly reduces the certificate size from 152,322 bytes to just 3,771 bytes, demonstrating a substantial decrease in size by over 40 times. Such minimization is particularly crucial in contexts with strict size limitations, like embedding certificate data in email headers.
 
 ## Identifying certificates: Fingerprints and Key IDs