diff --git a/nixos/modules/services/misc/nix-daemon.nix b/nixos/modules/services/misc/nix-daemon.nix
index e9aa10181789..e2548864af5b 100644
--- a/nixos/modules/services/misc/nix-daemon.nix
+++ b/nixos/modules/services/misc/nix-daemon.nix
@@ -82,9 +82,10 @@ in
         description = ''
           This option defines the maximum number of concurrent tasks during
           one build. It affects, e.g., -j option for make. The default is 1.
-          Some builds may become non-deterministic with this option; use with
-          care! Packages will only be affected if enableParallelBuilding is
-          set for them.
+          The special value 0 means that the builder should use all
+          available CPU cores in the system. Some builds may become
+          non-deterministic with this option; use with care! Packages will
+          only be affected if enableParallelBuilding is set for them.
         '';
       };