diff --git a/flake.nix b/flake.nix
index a455c5a94..ed0cad534 100644
--- a/flake.nix
+++ b/flake.nix
@@ -253,10 +253,11 @@
         pkgs.stdenv.mkDerivation {
           name = "artiq-board-${target}-${variant}";
           phases = [ "buildPhase" "checkPhase" "installPhase" ];
-          cargoDeps = rustPlatform.fetchCargoTarball {
-            name = "artiq-firmware-cargo-deps";
-            src = "${self}/artiq/firmware";
-            sha256 = "sha256-YyycMsDzR+JRcMZJd6A/CRi2J9nKmaWY/KXUnAQaZ00=";
+          cargoDeps = rustPlatform.importCargoLock {
+            lockFile = ./artiq/firmware/Cargo.lock;
+            outputHashes = {
+              "fringe-1.2.1" = "sha256-m4rzttWXRlwx53LWYpaKuU5AZe4GSkbjHS6oINt5d3Y=";
+            };
           };
           nativeBuildInputs = [
             (pkgs.python3.withPackages(ps: [ ps.jsonschema  migen misoc artiq]))