diff --git a/nixos/modules/services/networking/harmonia.nix b/nixos/modules/services/networking/harmonia.nix
index 0f9d328d0059..144fa6c708e2 100644
--- a/nixos/modules/services/networking/harmonia.nix
+++ b/nixos/modules/services/networking/harmonia.nix
@@ -1,7 +1,6 @@
 { config, pkgs, lib, ... }:
 let
   cfg = config.services.harmonia;
-
   format = pkgs.formats.toml { };
 in
 {
@@ -12,21 +11,23 @@ in
       signKeyPath = lib.mkOption {
         type = lib.types.nullOr lib.types.path;
         default = null;
-        description = lib.mdDoc "Path to the signing key to use for signing the cache";
+        description = lib.mdDoc "Path to the signing key that will be used for signing the cache";
       };
 
       package = lib.mkPackageOptionMD pkgs "harmonia" { };
 
       settings = lib.mkOption {
         inherit (format) type;
-        description = lib.mdDoc "Settings to merge with the default configuration";
+        default = { };
+        description = lib.mdDoc ''
+          Settings to merge with the default configuration.
+          For the list of the default configuration, see <https://github.com/nix-community/harmonia/tree/master#configuration>.
+        '';
       };
     };
   };
 
   config = lib.mkIf cfg.enable {
-    services.harmonia.settings.bind = lib.mkDefault "[::]:5000";
-
     systemd.services.harmonia = {
       description = "harmonia binary cache service";
 
@@ -45,17 +46,14 @@ in
 
       serviceConfig = {
         ExecStart = lib.getExe cfg.package;
-
         User = "harmonia";
         Group = "harmonia";
         DynamicUser = true;
         PrivateUsers = true;
         DeviceAllow = [ "" ];
         UMask = "0066";
-
         RuntimeDirectory = "harmonia";
-        LoadCredential = lib.optional (cfg.signKeyPath != null) "sign-key:${cfg.signKeyPath}";
-
+        LoadCredential = lib.mkIf (cfg.signKeyPath != null) [ "sign-key:${cfg.signKeyPath}" ];
         SystemCallFilter = [
           "@system-service"
           "~@privileged"
@@ -74,7 +72,6 @@ in
         ProtectProc = "invisible";
         RestrictNamespaces = true;
         SystemCallArchitectures = "native";
-
         PrivateNetwork = false;
         PrivateTmp = true;
         PrivateDevices = true;
@@ -84,7 +81,6 @@ in
         ProtectHome = true;
         LockPersonality = true;
         RestrictAddressFamilies = "AF_UNIX AF_INET AF_INET6";
-
         LimitNOFILE = 65536;
       };
     };
diff --git a/nixos/tests/all-tests.nix b/nixos/tests/all-tests.nix
index 5ceb39d0be51..5459dd161b81 100644
--- a/nixos/tests/all-tests.nix
+++ b/nixos/tests/all-tests.nix
@@ -297,7 +297,7 @@ in {
   haste-server = handleTest ./haste-server.nix {};
   haproxy = handleTest ./haproxy.nix {};
   hardened = handleTest ./hardened.nix {};
-  harmonia = handleTest ./harmonia.nix {};
+  harmonia = runTest ./harmonia.nix;
   headscale = handleTest ./headscale.nix {};
   healthchecks = handleTest ./web-apps/healthchecks.nix {};
   hbase2 = handleTest ./hbase.nix { package=pkgs.hbase2; };
diff --git a/nixos/tests/harmonia.nix b/nixos/tests/harmonia.nix
index 95fb7ea18cf8..3057caf70160 100644
--- a/nixos/tests/harmonia.nix
+++ b/nixos/tests/harmonia.nix
@@ -1,19 +1,20 @@
-import ./make-test-python.nix ({ pkgs, ... }:
+{ pkgs, lib, ... }:
+
 {
   name = "harmonia";
+
   nodes = {
     harmonia = {
       services.harmonia = {
         enable = true;
-        signKeyPath = pkgs.writeText "cache-key"
-          "cache.example.com-1:9FhO0w+7HjZrhvmzT1VlAZw4OSAlFGTgC24Seg3tmPl4gZBdwZClzTTHr9cVzJpwsRSYLTu7hEAQe3ljy92CWg==";
+        signKeyPath = pkgs.writeText "cache-key" "cache.example.com-1:9FhO0w+7HjZrhvmzT1VlAZw4OSAlFGTgC24Seg3tmPl4gZBdwZClzTTHr9cVzJpwsRSYLTu7hEAQe3ljy92CWg==";
       };
 
       networking.firewall.allowedTCPPorts = [ 5000 ];
-      system.extraDependencies = [ pkgs.hello ];
+      system.extraDependencies = [ pkgs.emptyFile ];
     };
 
-    client01 = { lib, ... }: {
+    client01 = {
       nix.settings = {
         substituters = lib.mkForce [ "http://harmonia:5000" ];
         trusted-public-keys = lib.mkForce [ "cache.example.com-1:eIGQXcGQpc00x6/XFcyacLEUmC07u4RAEHt5Y8vdglo=" ];
@@ -21,13 +22,14 @@ import ./make-test-python.nix ({ pkgs, ... }:
     };
   };
 
-  testScript = ''
+  testScript = { nodes, ... }: ''
     start_all()
 
-    client01.wait_until_succeeds("curl -f http://harmonia:5000/version")
-    client01.succeed("curl -f http://harmonia:5000/nix-cache-info")
+    harmonia.wait_for_unit("harmonia.service")
+    client01.wait_until_succeeds("curl -f http://harmonia:5000/nix-cache-info")
+    client01.succeed("curl -f http://harmonia:5000/version | grep '${nodes.harmonia.services.harmonia.package.version}' >&2")
 
     client01.succeed("cat /etc/nix/nix.conf >&2")
-    client01.wait_until_succeeds("nix-store --realise ${pkgs.hello} --store /root/other-store")
+    client01.succeed("nix-store --realise ${pkgs.emptyFile} --store /root/other-store")
   '';
-})
+}
diff --git a/pkgs/tools/package-management/harmonia/default.nix b/pkgs/tools/package-management/harmonia/default.nix
index 267b04a700aa..f3c121c7c734 100644
--- a/pkgs/tools/package-management/harmonia/default.nix
+++ b/pkgs/tools/package-management/harmonia/default.nix
@@ -11,16 +11,16 @@
 
 rustPlatform.buildRustPackage rec {
   pname = "harmonia";
-  version = "0.6.3";
+  version = "0.6.4";
 
   src = fetchFromGitHub {
     owner = "nix-community";
     repo = pname;
     rev = "refs/tags/${pname}-v${version}";
-    hash = "sha256-erBmPXMyIYxRLbYG35vH67MypJoXomUEFOVu6IhmEWs=";
+    hash = "sha256-JH0tdUCadvovAJclpx7Fn1oD+POFpBFHdullRTcFaVQ=";
   };
 
-  cargoHash = "sha256-Gq7U+Uy3psuPVY0wGM90KA5u5Wc2s4hVJma7B11Ag5g=";
+  cargoHash = "sha256-Wa+7Vo5VWmx47Uf6YtlzHReoWY44SxdOnscSFu74OSM=";
 
   nativeBuildInputs = [
     pkg-config nix