diff --git a/nixos/modules/services/mail/stalwart-mail.nix b/nixos/modules/services/mail/stalwart-mail.nix
index 42198573ec09..6622a2dcd114 100644
--- a/nixos/modules/services/mail/stalwart-mail.nix
+++ b/nixos/modules/services/mail/stalwart-mail.nix
@@ -107,21 +107,17 @@ in
       resolver.public-suffix = lib.mkDefault [
         "file://${pkgs.publicsuffix-list}/share/publicsuffix/public_suffix_list.dat"
       ];
-      config = {
-        spam-filter.resource = lib.mkDefault "file://${cfg.package}/etc/stalwart/spamfilter.toml";
-        webadmin =
-          let
-            hasHttpListener = builtins.any (listener: listener.protocol == "http") (
-              lib.attrValues cfg.settings.server.listener
-            );
-          in
-          {
-            path = "/var/cache/stalwart-mail";
-          }
-          // lib.optionalAttrs ((builtins.hasAttr "listener" cfg.settings.server) && hasHttpListener) {
-            resource = lib.mkDefault "file://${cfg.package.webadmin}/webadmin.zip";
-          };
-      };
+      spam-filter.resource = lib.mkDefault "file://${cfg.package}/etc/stalwart/spamfilter.toml";
+      webadmin =
+        let
+          hasHttpListener = builtins.any (listener: listener.protocol == "http") (
+            lib.attrValues (cfg.settings.server.listener or { })
+          );
+        in
+        {
+          path = "/var/cache/stalwart-mail";
+          resource = lib.mkIf (hasHttpListener) (lib.mkDefault "file://${cfg.package.webadmin}/webadmin.zip");
+        };
     };
 
     # This service stores a potentially large amount of data.
diff --git a/nixos/tests/stalwart-mail.nix b/nixos/tests/stalwart-mail.nix
index cfc0d3bb1c5b..361fd85e34a6 100644
--- a/nixos/tests/stalwart-mail.nix
+++ b/nixos/tests/stalwart-mail.nix
@@ -42,6 +42,11 @@ in
               bind = [ "[::]:143" ];
               protocol = "imap";
             };
+
+            "http" = {
+              bind = [ "[::]:80" ];
+              protocol = "http";
+            };
           };
 
           session.auth.mechanisms = "[plain]";
@@ -114,9 +119,13 @@ in
       main.wait_for_unit("stalwart-mail.service")
       main.wait_for_open_port(587)
       main.wait_for_open_port(143)
+      main.wait_for_open_port(80)
 
       main.succeed("test-smtp-submission")
       main.succeed("test-imap-read")
+
+      main.succeed("test -d /var/cache/stalwart-mail/STALWART_WEBADMIN")
+      main.succeed("curl --fail http://localhost")
     '';
 
   meta = {