diff --git a/doc/manual/src/hacking.md b/doc/manual/src/hacking.md
index 98a41a20..50f9339f 100644
--- a/doc/manual/src/hacking.md
+++ b/doc/manual/src/hacking.md
@@ -8,7 +8,7 @@ $ git clone git://github.com/NixOS/hydra.git
 $ cd hydra
 ```
 
-To enter a shell in which all environment variables (such as PERL5LIB)
+To enter a shell in which all environment variables (such as `PERL5LIB`)
 are set up so that those dependencies can be found:
 
 ```console