diff --git a/buildbot_nix/worker.py b/buildbot_nix/worker.py
index 0018915..17298a8 100644
--- a/buildbot_nix/worker.py
+++ b/buildbot_nix/worker.py
@@ -22,11 +22,14 @@ class WorkerConfig:
         .read_text()
         .rstrip("\r\n")
     )
-    worker_count: int = int(
-        os.environ.get("WORKER_COUNT", str(multiprocessing.cpu_count())),
-    )
-    worker_arch_list: list[str] = field(
-        default_factory=lambda: os.environ.get("WORKER_ARCH_LIST", "").split(",") + ["other"],
+    worker_arch_list: dict[str, int] = field(
+        default_factory=lambda: dict(other=1) | {
+            arch: int(count)
+            for arch, count in (
+                e.split("=")
+                for e in os.environ.get("WORKER_ARCH_LIST", "").split(",")
+            )
+        },
     )
     buildbot_dir: Path = field(
         default_factory=lambda: Path(require_env("BUILDBOT_DIR"))
@@ -70,8 +73,8 @@ def setup_worker(
 
 
 def setup_workers(application: components.Componentized, config: WorkerConfig) -> None:
-    for i in range(config.worker_count):
-        for arch in config.worker_arch_list:
+    for arch, jobs in config.worker_arch_list.items():
+        for i in range(jobs):
             setup_worker(application, i, arch, config)
 
 
diff --git a/nix/worker.nix b/nix/worker.nix
index bbbfd81..3be1b3b 100644
--- a/nix/worker.nix
+++ b/nix/worker.nix
@@ -28,8 +28,8 @@ in
         type = lib.types.path;
         description = "The buildbot worker password file.";
       };
-      workerArchList = lib.mkOption {
-        type = lib.types.listOf lib.types.str;
+      workerArchitectures = lib.mkOption {
+        type = lib.types.attrsOf lib.types.int;
         description = "Nix `system`s the worker should feel responsible for.";
       };
     };
@@ -66,6 +66,9 @@ in
       environment.PYTHONPATH = "${python.withPackages (_: [cfg.package])}/${python.sitePackages}";
       environment.MASTER_URL = cfg.coordinatorUrl;
       environment.BUILDBOT_DIR = buildbotDir;
+      environment.WORKER_ARCH_LIST =
+        lib.concatStringsSep ","
+          (lib.mapAttrsToList (arch: jobs: "${arch}=${toString jobs}") cfg.workerArchitectures);
 
       serviceConfig = {
         # We rather want the CI job to fail on OOM than to have a broken buildbot worker.
@@ -75,7 +78,6 @@ in
         LoadCredential = [ "worker-password-file:${cfg.workerPasswordFile}" ];
         Environment = [
           "WORKER_PASSWORD_FILE=%d/worker-password-file"
-          "WORKER_ARCH_LIST=${lib.concatStringsSep "," cfg.workerArchList}"
         ];
         Type = "simple";
         User = "buildbot-worker";