diff --git a/pkgs/games/factorio/default.nix b/pkgs/games/factorio/default.nix
index 0226acf1604..e5527c9d4ef 100644
--- a/pkgs/games/factorio/default.nix
+++ b/pkgs/games/factorio/default.nix
@@ -104,10 +104,15 @@ let
               ];
             })
             (_: { # This preHook hides the credentials from /proc
-                  preHook = ''
-                    echo -n "${username}" >username
-                    echo -n "${token}"    >token
-                  '';
+                  preHook =
+                    if username != "" && token != "" then ''
+                      echo -n "${username}" >username
+                      echo -n "${token}"    >token
+                    '' else ''
+                      # Deliberately failing since username/token was not provided, so we can't fetch.
+                      # We can't use builtins.throw since we want the result to be used if the tar is in the store already.
+                      exit 1
+                    '';
                   failureHook = ''
                     cat <<EOF
                     ${helpMsg}