diff --git a/nixops/desktop.nix b/nixops/desktop.nix
index e6cd91b9..c6c97db8 100644
--- a/nixops/desktop.nix
+++ b/nixops/desktop.nix
@@ -166,7 +166,7 @@ in
   services.udev.extraRules = (import ./extra-udev.nix);
 
   nix.settings.trusted-public-keys = ["nixbld.m-labs.hk-1:5aSRVA5b320xbNvu30tqxVPXpld73bhtOeH6uAjRyHc="];
-  nix.settings.substituters = ["https://nixbld.m-labs.hk" "https://cache.nixos.org"];
+  nix.settings.substituters = ["https://nixbld.m-labs.hk?priority=10"];
   nix.settings.extra-sandbox-paths = ["/opt"];
 
   nix.extraOptions = ''
diff --git a/nixops/rpi.nix b/nixops/rpi.nix
index 5ea3e742..e50abb2e 100644
--- a/nixops/rpi.nix
+++ b/nixops/rpi.nix
@@ -66,7 +66,7 @@ in
   programs.wireshark.enable = true;
 
   nix.settings.trusted-public-keys = ["nixbld.m-labs.hk-1:5aSRVA5b320xbNvu30tqxVPXpld73bhtOeH6uAjRyHc="];
-  nix.settings.substituters = ["https://nixbld.m-labs.hk" "https://cache.nixos.org"];
+  nix.settings.substituters = ["https://nixbld.m-labs.hk?priority=10"];
   nix.settings.trusted-users = ["root" "sb"];
 
   nix.extraOptions = ''