diff --git a/modules/services/syncthing.nix b/modules/services/syncthing.nix
index 839ec9b16..125b05f3c 100644
--- a/modules/services/syncthing.nix
+++ b/modules/services/syncthing.nix
@@ -25,6 +25,10 @@ let
     else
       "\${XDG_STATE_HOME:-$HOME/.local/state}/syncthing";
 
+  defaultGuiAddress = "127.0.0.1:8384";
+
+  hasCustomGuiAddress = cfg.guiAddress != defaultGuiAddress;
+
   # Syncthing supports serving the GUI over Unix sockets. If that happens, the
   # API is served over the Unix socket as well.  This function returns the correct
   # curl arguments for the address portion of the curl command for both network
@@ -288,7 +292,7 @@ let
         ''))
         (lib.concatStringsSep "\n")
       ])
-    + lib.optionalString (cfg.guiAddress != null) ''
+    + lib.optionalString hasCustomGuiAddress ''
       curl -X PATCH -d '{"address": "'${cfg.guiAddress}'"}' ${curlAddressArgs "/rest/config/gui"}
     ''
     + ''
@@ -300,7 +304,7 @@ let
     ''
   );
 
-  doUpdateConfig = cleanedConfig != { } || cfg.guiCredentials != null || cfg.guiAddress != null;
+  doUpdateConfig = cleanedConfig != { } || cfg.guiCredentials != null || hasCustomGuiAddress;
 
   defaultSyncthingArgs = [
     "${syncthing}"
@@ -771,7 +775,7 @@ in
 
       guiAddress = mkOption {
         type = types.str;
-        default = "127.0.0.1:8384";
+        default = defaultGuiAddress;
         description = ''
           The address to serve the web interface at.
         '';
diff --git a/tests/modules/services/syncthing/extra-options.nix b/tests/modules/services/syncthing/extra-options.nix
index 8f80b6aa4..e59b440ab 100644
--- a/tests/modules/services/syncthing/extra-options.nix
+++ b/tests/modules/services/syncthing/extra-options.nix
@@ -18,6 +18,8 @@ lib.mkMerge [
   (lib.mkIf pkgs.stdenv.isLinux {
     nmt.script = ''
       assertFileExists home-files/.config/systemd/user/syncthing.service
+      assertPathNotExists home-files/.config/systemd/user/syncthing-init.service
+      assertPathNotExists home-files/.config/systemd/user/default.target.wants/syncthing-init.service
       assertFileContains home-files/.config/systemd/user/syncthing.service \
       "ExecStart=@syncthing@/bin/syncthing serve --no-browser --no-restart --no-upgrade '--gui-address=127.0.0.1:8384' -foo '-bar \"baz\"'"
     '';
@@ -27,6 +29,7 @@ lib.mkMerge [
     nmt.script = ''
       serviceFile=LaunchAgents/org.nix-community.home.syncthing.plist
       assertFileExists "$serviceFile"
+      assertPathNotExists LaunchAgents/org.nix-community.home.syncthing-init.plist
       assertFileContent "$serviceFile" ${./expected-agent.plist}
     '';
   })
diff --git a/tests/modules/services/syncthing/linux/default.nix b/tests/modules/services/syncthing/linux/default.nix
index da4505040..cd3c7ab59 100644
--- a/tests/modules/services/syncthing/linux/default.nix
+++ b/tests/modules/services/syncthing/linux/default.nix
@@ -1,3 +1,4 @@
 {
+  syncthing-gui-address-init = ./gui-address-init.nix;
   syncthing-tray = ./tray.nix;
 }
diff --git a/tests/modules/services/syncthing/linux/gui-address-init.nix b/tests/modules/services/syncthing/linux/gui-address-init.nix
new file mode 100644
index 000000000..24cbd9a2c
--- /dev/null
+++ b/tests/modules/services/syncthing/linux/gui-address-init.nix
@@ -0,0 +1,16 @@
+{
+  services.syncthing = {
+    enable = true;
+    guiAddress = "127.0.0.1:8385";
+  };
+
+  nmt.script = ''
+    serviceFile=home-files/.config/systemd/user/syncthing-init.service
+    assertFileExists "$serviceFile"
+    assertFileExists home-files/.config/systemd/user/default.target.wants/syncthing-init.service
+    assertFileContains "$serviceFile" "ExecStart="
+
+    updateScript=$(grep -o '/nix/store/[^ ]*-merge-syncthing-config' "$TESTED/$serviceFile")
+    assertFileContains "$updateScript" "127.0.0.1:8385/rest/config/gui"
+  '';
+}