diff --git a/frontend/src/lib/components/form/form-input.svelte b/frontend/src/lib/components/form/form-input.svelte
index 4be4688a..0d768eb4 100644
--- a/frontend/src/lib/components/form/form-input.svelte
+++ b/frontend/src/lib/components/form/form-input.svelte
@@ -17,7 +17,7 @@
 		onInput,
 		...restProps
 	}: HTMLAttributes<HTMLDivElement> & {
-		input?: FormInput<string | boolean | number | Date>;
+		input?: FormInput<string | boolean | number | Date | undefined>;
 		label?: string;
 		description?: string;
 		placeholder?: string;
diff --git a/frontend/src/routes/settings/account/account-form.svelte b/frontend/src/routes/settings/account/account-form.svelte
index c294edba..c7df8ecd 100644
--- a/frontend/src/routes/settings/account/account-form.svelte
+++ b/frontend/src/routes/settings/account/account-form.svelte
@@ -28,7 +28,7 @@
 
 	const formSchema = z.object({
 		firstName: z.string().min(1).max(50),
-		lastName: z.string().max(50),
+		lastName: z.string().max(50).optional(),
 		username: z
 			.string()
 			.min(2)
diff --git a/frontend/src/routes/settings/admin/users/[id]/+page.svelte b/frontend/src/routes/settings/admin/users/[id]/+page.svelte
index f9ae682f..ae13e5cf 100644
--- a/frontend/src/routes/settings/admin/users/[id]/+page.svelte
+++ b/frontend/src/routes/settings/admin/users/[id]/+page.svelte
@@ -6,6 +6,7 @@
 	import { Button } from '$lib/components/ui/button';
 	import * as Card from '$lib/components/ui/card';
 	import UserGroupSelection from '$lib/components/user-group-selection.svelte';
+	import { m } from '$lib/paraglide/messages';
 	import CustomClaimService from '$lib/services/custom-claim-service';
 	import UserService from '$lib/services/user-service';
 	import appConfigStore from '$lib/stores/application-configuration-store';
@@ -14,7 +15,6 @@
 	import { LucideChevronLeft } from 'lucide-svelte';
 	import { toast } from 'svelte-sonner';
 	import UserForm from '../user-form.svelte';
-	import { m } from '$lib/paraglide/messages';
 
 	let { data } = $props();
 	let user = $state({
@@ -75,7 +75,7 @@
 	<title
 		>{m.user_details_firstname_lastname({
 			firstName: user.firstName,
-			lastName: user.lastName
+			lastName: user.lastName ?? ''
 		})}</title
 	>
 </svelte:head>
diff --git a/frontend/src/routes/settings/admin/users/user-list.svelte b/frontend/src/routes/settings/admin/users/user-list.svelte
index 89008f23..c8385b41 100644
--- a/frontend/src/routes/settings/admin/users/user-list.svelte
+++ b/frontend/src/routes/settings/admin/users/user-list.svelte
@@ -34,7 +34,7 @@
 
 	async function deleteUser(user: User) {
 		openConfirmDialog({
-			title: m.delete_firstname_lastname({ firstName: user.firstName, lastName: user.lastName }),
+			title: m.delete_firstname_lastname({ firstName: user.firstName, lastName: user.lastName ?? "" }),
 			message: m.are_you_sure_you_want_to_delete_this_user(),
 			confirm: {
 				label: m.delete(),
@@ -67,7 +67,7 @@
 
 	async function disableUser(user: User) {
 		openConfirmDialog({
-			title: m.disable_firstname_lastname({ firstName: user.firstName, lastName: user.lastName }),
+			title: m.disable_firstname_lastname({ firstName: user.firstName, lastName: user.lastName ?? "" }),
 			message: m.are_you_sure_you_want_to_disable_this_user(),
 			confirm: {
 				label: m.disable(),