diff --git a/source/tutorials/building-and-running-docker-images.rst b/source/tutorials/building-and-running-docker-images.rst
index e3918c8..de4f7b2 100644
--- a/source/tutorials/building-and-running-docker-images.rst
+++ b/source/tutorials/building-and-running-docker-images.rst
@@ -24,7 +24,7 @@ Docker images:
 
 .. code:: nix
 
-    { pkgs ? import <nixpkgs> {} }:
+    { pkgs ? import <nixpkgs> { system = "x86_64-linux"; } }:
 
     pkgs.dockerTools.buildImage {
       name = "hello-docker";