diff --git a/flake.nix b/flake.nix
index bb668ed..9f2fc19 100644
--- a/flake.nix
+++ b/flake.nix
@@ -163,7 +163,8 @@
         checks.tests = craneLib.cargoTest (hostArgs // {
           cargoArtifacts = hostArtifacts;
           cargoExtraArgs = "--locked -p sausage -p sausage-vfs";
-          cargoTestExtraArgs = "-- --nocapture";
+          # Guest builds and cold compilations share the check's CPU and memory.
+          cargoTestExtraArgs = "-- --nocapture --test-threads=1";
           doCheck = true;
           nativeBuildInputs = hostArgs.nativeBuildInputs ++ builderTools ++ [ pkgs.git pkgs.nodejs ];
           SAUSAGE_TEST_NO_BUILDER_SANDBOX = "1";