diff --git a/modules/services/syncthing.nix b/modules/services/syncthing.nix
index d2f7f2964..fd9e34180 100644
--- a/modules/services/syncthing.nix
+++ b/modules/services/syncthing.nix
@@ -9,6 +9,15 @@ with lib;
     services.syncthing = {
       enable = mkEnableOption "Syncthing continuous file synchronization";
 
+      extraOptions = mkOption {
+        type = types.listOf types.str;
+        default = [ ];
+        example = [ "--gui-apikey=apiKey" ];
+        description = ''
+          Extra command-line arguments to pass to <command>syncthing</command>.
+        '';
+      };
+
       tray = mkOption {
         type = with types;
           either bool (submodule {
@@ -57,7 +66,9 @@ with lib;
 
           Service = {
             ExecStart =
-              "${pkgs.syncthing}/bin/syncthing -no-browser -no-restart -logflags=0";
+              "${pkgs.syncthing}/bin/syncthing -no-browser -no-restart -logflags=0"
+              + optionalString (config.services.syncthing.extraOptions != [ ])
+              (" " + escapeShellArgs config.services.syncthing.extraOptions);
             Restart = "on-failure";
             SuccessExitStatus = [ 3 4 ];
             RestartForceExitStatus = [ 3 4 ];
diff --git a/tests/modules/services/syncthing/default.nix b/tests/modules/services/syncthing/default.nix
index 14136fe63..86f72b571 100644
--- a/tests/modules/services/syncthing/default.nix
+++ b/tests/modules/services/syncthing/default.nix
@@ -1,4 +1,5 @@
 {
+  syncthing-extra-options = ./extra-options.nix;
   syncthing-tray = ./tray.nix;
   syncthing-tray-as-bool-triggers-warning = ./tray-as-bool-triggers-warning.nix;
 }
diff --git a/tests/modules/services/syncthing/extra-options.nix b/tests/modules/services/syncthing/extra-options.nix
new file mode 100644
index 000000000..c78b00f9c
--- /dev/null
+++ b/tests/modules/services/syncthing/extra-options.nix
@@ -0,0 +1,16 @@
+{ config, ... }:
+
+{
+  services.syncthing = {
+    enable = true;
+    extraOptions = [ "-foo" ''-bar "baz"'' ];
+  };
+
+  test.stubs.syncthing = { };
+
+  nmt.script = ''
+    assertFileExists home-files/.config/systemd/user/syncthing.service
+    assertFileContains home-files/.config/systemd/user/syncthing.service \
+      "ExecStart=@syncthing@/bin/syncthing -no-browser -no-restart -logflags=0 '-foo' '-bar \"baz\"'"
+  '';
+}