diff --git a/nixos/modules/services/cluster/kubernetes/kubelet.nix b/nixos/modules/services/cluster/kubernetes/kubelet.nix
index 5dcd18293488..0898fee9bdb7 100644
--- a/nixos/modules/services/cluster/kubernetes/kubelet.nix
+++ b/nixos/modules/services/cluster/kubernetes/kubelet.nix
@@ -177,8 +177,7 @@ in
 
     hostname = mkOption {
       description = lib.mdDoc "Kubernetes kubelet hostname override.";
-      default = config.networking.hostName;
-      defaultText = literalExpression "config.networking.hostName";
+      defaultText = literalExpression "config.networking.fqdnOrHostName";
       type = str;
     };
 
@@ -349,8 +348,8 @@ in
 
       boot.kernelModules = ["br_netfilter" "overlay"];
 
-      services.kubernetes.kubelet.hostname = with config.networking;
-        mkDefault (hostName + optionalString (domain != null) ".${domain}");
+      services.kubernetes.kubelet.hostname =
+        mkDefault config.networking.fqdnOrHostName;
 
       services.kubernetes.pki.certs = with top.lib; {
         kubelet = mkCert {
diff --git a/nixos/modules/services/monitoring/smartd.nix b/nixos/modules/services/monitoring/smartd.nix
index cfebb4b9798b..1e654cad5dd2 100644
--- a/nixos/modules/services/monitoring/smartd.nix
+++ b/nixos/modules/services/monitoring/smartd.nix
@@ -4,8 +4,7 @@ with lib;
 
 let
 
-  host = config.networking.hostName or "unknown"
-       + optionalString (config.networking.domain != null) ".${config.networking.domain}";
+  host = config.networking.fqdnOrHostName;
 
   cfg = config.services.smartd;
   opt = options.services.smartd;
diff --git a/nixos/modules/services/networking/flannel.nix b/nixos/modules/services/networking/flannel.nix
index c19e51e5aa6c..6ed4f78ddc92 100644
--- a/nixos/modules/services/networking/flannel.nix
+++ b/nixos/modules/services/networking/flannel.nix
@@ -92,10 +92,8 @@ in {
         Needed when running with Kubernetes as backend as this cannot be auto-detected";
       '';
       type = types.nullOr types.str;
-      default = with config.networking; (hostName + optionalString (domain != null) ".${domain}");
-      defaultText = literalExpression ''
-        with config.networking; (hostName + optionalString (domain != null) ".''${domain}")
-      '';
+      default = config.networking.fqdnOrHostName;
+      defaultText = literalExpression "config.networking.fqdnOrHostName";
       example = "node1.example.com";
     };
 
diff --git a/nixos/modules/services/networking/jitsi-videobridge.nix b/nixos/modules/services/networking/jitsi-videobridge.nix
index eefaa70604cd..09f2ddf92c5c 100644
--- a/nixos/modules/services/networking/jitsi-videobridge.nix
+++ b/nixos/modules/services/networking/jitsi-videobridge.nix
@@ -150,7 +150,7 @@ in
         config = {
           hostName = mkDefault name;
           mucNickname = mkDefault (builtins.replaceStrings [ "." ] [ "-" ] (
-            config.networking.hostName + optionalString (config.networking.domain != null) ".${config.networking.domain}"
+            config.networking.fqdnOrHostName
           ));
         };
       }));
diff --git a/nixos/modules/services/web-apps/bookstack.nix b/nixos/modules/services/web-apps/bookstack.nix
index eeef77727769..40bb377e2c88 100644
--- a/nixos/modules/services/web-apps/bookstack.nix
+++ b/nixos/modules/services/web-apps/bookstack.nix
@@ -60,11 +60,8 @@ in {
 
     hostname = lib.mkOption {
       type = lib.types.str;
-      default = if config.networking.domain != null then
-                  config.networking.fqdn
-                else
-                  config.networking.hostName;
-      defaultText = lib.literalExpression "config.networking.fqdn";
+      default = config.networking.fqdnOrHostName;
+      defaultText = lib.literalExpression "config.networking.fqdnOrHostName";
       example = "bookstack.example.com";
       description = lib.mdDoc ''
         The hostname to serve BookStack on.
diff --git a/nixos/modules/services/web-apps/discourse.nix b/nixos/modules/services/web-apps/discourse.nix
index 9ad451f31f74..6500b8cad217 100644
--- a/nixos/modules/services/web-apps/discourse.nix
+++ b/nixos/modules/services/web-apps/discourse.nix
@@ -42,11 +42,8 @@ in
 
       hostname = lib.mkOption {
         type = lib.types.str;
-        default = if config.networking.domain != null then
-                    config.networking.fqdn
-                  else
-                    config.networking.hostName;
-        defaultText = lib.literalExpression "config.networking.fqdn";
+        default = config.networking.fqdnOrHostName;
+        defaultText = lib.literalExpression "config.networking.fqdnOrHostName";
         example = "discourse.example.com";
         description = lib.mdDoc ''
           The hostname to serve Discourse on.
diff --git a/nixos/modules/services/web-apps/matomo.nix b/nixos/modules/services/web-apps/matomo.nix
index 9e8d85161da7..117d540ba36b 100644
--- a/nixos/modules/services/web-apps/matomo.nix
+++ b/nixos/modules/services/web-apps/matomo.nix
@@ -12,8 +12,6 @@ let
   phpExecutionUnit = "phpfpm-${pool}";
   databaseService = "mysql.service";
 
-  fqdn = if config.networking.domain != null then config.networking.fqdn else config.networking.hostName;
-
 in {
   imports = [
     (mkRenamedOptionModule [ "services" "piwik" "enable" ] [ "services" "matomo" "enable" ])
@@ -77,11 +75,9 @@ in {
 
       hostname = mkOption {
         type = types.str;
-        default = "${user}.${fqdn}";
+        default = "${user}.${config.networking.fqdnOrHostName}";
         defaultText = literalExpression ''
-          if config.${options.networking.domain} != null
-          then "${user}.''${config.${options.networking.fqdn}}"
-          else "${user}.''${config.${options.networking.hostName}}"
+          "${user}.''${config.${options.networking.fqdnOrHostName}}"
         '';
         example = "matomo.yourdomain.org";
         description = lib.mdDoc ''
diff --git a/nixos/modules/services/web-apps/snipe-it.nix b/nixos/modules/services/web-apps/snipe-it.nix
index e0d2eb8c6ab2..6da44f1bdf34 100644
--- a/nixos/modules/services/web-apps/snipe-it.nix
+++ b/nixos/modules/services/web-apps/snipe-it.nix
@@ -54,11 +54,8 @@ in {
 
     hostName = lib.mkOption {
       type = lib.types.str;
-      default = if config.networking.domain != null then
-                  config.networking.fqdn
-                else
-                  config.networking.hostName;
-      defaultText = lib.literalExpression "config.networking.fqdn";
+      default = config.networking.fqdnOrHostName;
+      defaultText = lib.literalExpression "config.networking.fqdnOrHostName";
       example = "snipe-it.example.com";
       description = lib.mdDoc ''
         The hostname to serve Snipe-IT on.
diff --git a/nixos/modules/tasks/network-interfaces.nix b/nixos/modules/tasks/network-interfaces.nix
index 1982175eac94..b7a4282f9727 100644
--- a/nixos/modules/tasks/network-interfaces.nix
+++ b/nixos/modules/tasks/network-interfaces.nix
@@ -473,9 +473,29 @@ in
       defaultText = literalExpression ''"''${networking.hostName}.''${networking.domain}"'';
       description = lib.mdDoc ''
         The fully qualified domain name (FQDN) of this host. It is the result
-        of combining networking.hostName and networking.domain. Using this
+        of combining `networking.hostName` and `networking.domain.` Using this
         option will result in an evaluation error if the hostname is empty or
         no domain is specified.
+
+        Modules that accept a mere `networing.hostName` but prefer a fully qualified
+        domain name may use `networking.fqdnOrHostName` instead.
+      '';
+    };
+
+    networking.fqdnOrHostName = mkOption {
+      readOnly = true;
+      type = types.str;
+      default = if cfg.domain == null then cfg.hostName else cfg.fqdn;
+      defaultText = literalExpression ''
+        if cfg.domain == null then cfg.hostName else cfg.fqdn
+      '';
+      description = lib.mdDoc ''
+        Either the fully qualified domain name (FQDN), or just the host name if
+        it does not exists.
+
+        This is a convenience option for modules to read instead of `fqdn` when
+        a mere `hostName` is also an acceptable value; this option does not
+        throw an error when `domain` is unset.
       '';
     };