diff --git a/nixos/doc/manual/development/writing-nixos-tests.xml b/nixos/doc/manual/development/writing-nixos-tests.xml
index 5935fbc049b..983f8f9cbe3 100644
--- a/nixos/doc/manual/development/writing-nixos-tests.xml
+++ b/nixos/doc/manual/development/writing-nixos-tests.xml
@@ -108,7 +108,7 @@ xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualis
 <programlisting>
 $machine->start;
 $machine->waitForUnit("default.target");
-$machine->succeed("uname") =~ /Linux/;
+die unless $machine->succeed("uname") =~ /Linux/;
 </programlisting>
   The first line is actually unnecessary; machines are implicitly started when
   you first execute an action on them (such as <literal>waitForUnit</literal>