diff --git a/modules/examples/simple.nix b/modules/examples/simple.nix
index 09767f9..e81e95b 100644
--- a/modules/examples/simple.nix
+++ b/modules/examples/simple.nix
@@ -13,6 +13,10 @@
   # Recreate /run/current-system symlink after boot.
   services.activate-system.enable = true;
 
+  # Used for backwards compatibility, please read the changelog before changing.
+  # $ darwin-rebuild changelog
+  system.stateVersion = 2;
+
   # You should generally set this to the total number of logical cores in your system.
   # $ sysctl -n hw.ncpu
   nix.maxJobs = 1;