diff --git a/nixos/lib/testing.nix b/nixos/lib/testing.nix
index 59d05f87d5f..aa1cec1ea02 100644
--- a/nixos/lib/testing.nix
+++ b/nixos/lib/testing.nix
@@ -15,6 +15,8 @@ rec {
 
     unpackPhase = "true";
 
+    preferLocalBuild = true;
+
     installPhase =
       ''
         mkdir -p $out/bin