diff --git a/buildbot_nix/__init__.py b/buildbot_nix/__init__.py
index 2293d64..f4ebbc0 100644
--- a/buildbot_nix/__init__.py
+++ b/buildbot_nix/__init__.py
@@ -413,7 +413,8 @@ def nix_eval_config(
     github_token_secret: str,
     supported_systems: list[str],
     eval_lock: util.WorkerLock,
-    max_memory_size: int = 4096,
+    worker_count: int,
+    max_memory_size: int,
 ) -> util.BuilderConfig:
     """
     Uses nix-eval-jobs to evaluate hydraJobs from flake.nix in parallel.
@@ -441,7 +442,7 @@ def nix_eval_config(
             command=[
                 "nix-eval-jobs",
                 "--workers",
-                multiprocessing.cpu_count(),
+                str(worker_count),
                 "--max-memory-size",
                 str(max_memory_size),
                 "--option",
@@ -586,6 +587,7 @@ def config_for_project(
     worker_names: list[str],
     github: GithubConfig,
     nix_supported_systems: list[str],
+    nix_eval_worker_count: int,
     nix_eval_max_memory_size: int,
     eval_lock: util.WorkerLock,
     outputs_path: Path | None = None,
@@ -678,6 +680,7 @@ def config_for_project(
                 [worker_names[0]],
                 github_token_secret=github.token_secret_name,
                 supported_systems=nix_supported_systems,
+                worker_count=nix_eval_worker_count,
                 max_memory_size=nix_eval_max_memory_size,
                 eval_lock=eval_lock,
             ),
@@ -708,13 +711,15 @@ class NixConfigurator(ConfiguratorBase):
         github: GithubConfig,
         url: str,
         nix_supported_systems: list[str],
-        nix_eval_max_memory_size: int = 4096,
+        nix_eval_worker_count: int | None,
+        nix_eval_max_memory_size: int,
         nix_workers_secret_name: str = "buildbot-nix-workers",
         outputs_path: str | None = None,
     ) -> None:
         super().__init__()
         self.nix_workers_secret_name = nix_workers_secret_name
         self.nix_eval_max_memory_size = nix_eval_max_memory_size
+        self.nix_eval_worker_count = nix_eval_worker_count
         self.nix_supported_systems = nix_supported_systems
         self.github = github
         self.url = url
@@ -762,6 +767,7 @@ class NixConfigurator(ConfiguratorBase):
                 worker_names,
                 self.github,
                 self.nix_supported_systems,
+                self.nix_eval_worker_count or multiprocessing.cpu_count(),
                 self.nix_eval_max_memory_size,
                 eval_lock,
                 self.outputs_path,
@@ -816,7 +822,7 @@ class NixConfigurator(ConfiguratorBase):
         if not config["www"].get("auth"):
             config["www"]["avatar_methods"] = config["www"].get("avatar_methods", [])
             config["www"]["avatar_methods"].append(
-                util.AvatarGitHub(self.github.token())
+                util.AvatarGitHub(token=self.github.token())
             )
             config["www"]["auth"] = util.GitHubAuth(
                 self.github.oauth_id, read_secret_file(self.github.oauth_secret_name)
diff --git a/examples/default.nix b/examples/default.nix
index 1d619d9..b1d4ac8 100644
--- a/examples/default.nix
+++ b/examples/default.nix
@@ -38,6 +38,10 @@ in
           };
           # optional
           # outputsPath = "/var/www/buildbot/nix-outputs";
+
+          # optional nix-eval-jobs settings
+          # evalWorkerCount = 8; # limit number of concurrent evaluations
+          # evalMaxMemorySize = "2048"; # limit memory usage per evaluation
         };
       })
       buildbot-nix.nixosModules.buildbot-master
diff --git a/nix/master.nix b/nix/master.nix
index 3bdc584..3d82dc0 100644
--- a/nix/master.nix
+++ b/nix/master.nix
@@ -75,6 +75,14 @@ in
           restarted.
         '';
       };
+      evalWorkerCount = lib.mkOption {
+        type = lib.types.nullOr lib.types.int;
+        default = null;
+        description = ''
+          Number of nix-eval-jobs worker processes. If null, the number of cores is used.
+          If you experience memory issues (buildbot-workers going out-of-memory), you can reduce this number.
+        '';
+      };
       domain = lib.mkOption {
         type = lib.types.str;
         description = "Buildbot domain";
@@ -141,6 +149,7 @@ in
               ),
               url=${builtins.toJSON config.services.buildbot-master.buildbotUrl},
               nix_eval_max_memory_size=${builtins.toJSON cfg.evalMaxMemorySize},
+              nix_eval_worker_count=${builtins.toJSON cfg.evalWorkerCount},
               nix_supported_systems=${builtins.toJSON cfg.buildSystems},
               outputs_path=${if cfg.outputsPath == null then "None" else builtins.toJSON cfg.outputsPath},
           )