diff --git a/nixos/modules/installer/cd-dvd/channel.nix b/nixos/modules/installer/cd-dvd/channel.nix
index ab5e7c0645f..92164d65e53 100644
--- a/nixos/modules/installer/cd-dvd/channel.nix
+++ b/nixos/modules/installer/cd-dvd/channel.nix
@@ -21,7 +21,9 @@ let
       if [ ! -e $out/nixos/nixpkgs ]; then
         ln -s . $out/nixos/nixpkgs
       fi
-      echo -n ${config.system.nixos.revision} > $out/nixos/.git-revision
+      ${optionalString (config.system.nixos.revision != null) ''
+        echo -n ${config.system.nixos.revision} > $out/nixos/.git-revision
+      ''}
       echo -n ${config.system.nixos.versionSuffix} > $out/nixos/.version-suffix
       echo ${config.system.nixos.versionSuffix} | sed -e s/pre// > $out/nixos/svn-revision
     '';