diff --git a/apps/files_sharing/src/views/SharingDetailsTab.vue b/apps/files_sharing/src/views/SharingDetailsTab.vue
index c1cc67ca72289..aa858f0a70c33 100644
--- a/apps/files_sharing/src/views/SharingDetailsTab.vue
+++ b/apps/files_sharing/src/views/SharingDetailsTab.vue
@@ -167,6 +167,7 @@
 					<NcDateTimePickerNative
 						v-if="hasExpirationDate"
 						id="share-date-picker"
+						ref="expireDate"
 						:model-value="new Date(share.expireDate ?? dateTomorrow)"
 						:min="dateTomorrow"
 						:max="maxExpirationDateEnforced"
@@ -174,7 +175,8 @@
 						:label="t('files_sharing', 'Expiration date')"
 						:placeholder="t('files_sharing', 'Expiration date')"
 						type="date"
-						@input="onExpirationChange" />
+						@update:model-value="onExpirationChange"
+						@change="checkExpirationDateValidity" />
 					<NcCheckboxRadioSwitch
 						v-if="isPublicShare"
 						v-model="share.hideDownload"
@@ -878,6 +880,32 @@ export default {
 	},
 
 	methods: {
+		/**
+		 * Check native `min` / `max` constraints on the expiration date field.
+		 * Prefer the change event target when available (same pattern as SharingEntryLink).
+		 *
+		 * @param {Event} [event]
+		 * @return {boolean}
+		 */
+		checkExpirationDateValidity(event) {
+			const fromEvent = event?.target
+			const fromRef = this.$refs.expireDate?.$el?.querySelector?.('input')
+			const input = fromEvent instanceof HTMLInputElement
+				? fromEvent
+				: (fromRef instanceof HTMLInputElement ? fromRef : null)
+
+			if (!input) {
+				return true
+			}
+
+			input.setCustomValidity('')
+			const isValid = input.checkValidity()
+			if (!isValid) {
+				input.reportValidity()
+			}
+			return isValid
+		},
+
 		/**
 		 * Set a share attribute on the current share
 		 *
@@ -1101,6 +1129,8 @@ export default {
 
 			if (!this.hasExpirationDate) {
 				this.share.expireDate = ''
+			} else if (!this.checkExpirationDateValidity()) {
+				return
 			}
 
 			if (this.isNewShare) {
@@ -1449,4 +1479,9 @@ export default {
 		}
 	}
 }
+
+:deep(input:user-invalid) {
+	--input-border-color: var(--color-border-error, var(--color-error)) !important;
+	border-color: var(--color-border-error, var(--color-error)) !important;
+}
 </style>
diff --git a/apps/settings/src/components/Users/UserFormFields.vue b/apps/settings/src/components/Users/UserFormFields.vue
index 2e408e8329b6e..5e41946e968a9 100644
--- a/apps/settings/src/components/Users/UserFormFields.vue
+++ b/apps/settings/src/components/Users/UserFormFields.vue
@@ -30,7 +30,9 @@
 			autocomplete="off"
 			spellcheck="false"
 			pattern="[a-zA-Z0-9 _\.@\-']+"
-			:required="fieldConfig.username?.required" />
+			:required="fieldConfig.username?.required"
+			@input="updateUsernameValidity"
+			@blur="updateUsernameValidity" />
 
 		<NcTextField
 			v-model="formData.displayName"
@@ -138,6 +140,24 @@ const password = ref<{ focus?: () => void } | null>(null)
 
 const minPasswordLength = computed(() => store.getters.getPasswordPolicyMinLength)
 
+/**
+ * Customize the browser-native constraint validation message.
+ *
+ * @param event Input/blur event from the underlying input element
+ */
+function updateUsernameValidity(event: Event) {
+	const input = event.target as HTMLInputElement | null
+	if (!input) {
+		return
+	}
+
+	// Clear first so native constraint flags are evaluated without a stale customError.
+	input.setCustomValidity('')
+	if (input.validity.patternMismatch) {
+		input.setCustomValidity(t('settings', 'Only letters, numbers, spaces, and _.@-\' are allowed'))
+	}
+}
+
 // Errors not bound to a dedicated input, shown in the catch-all live region.
 const unhandledErrors = computed(() => {
 	const handled = new Set(['displayName', 'password', 'email'])
diff --git a/core/src/components/login/LoginForm.vue b/core/src/components/login/LoginForm.vue
index 4a350907db74c..c71d74e93865c 100644
--- a/core/src/components/login/LoginForm.vue
+++ b/core/src/components/login/LoginForm.vue
@@ -63,7 +63,7 @@
 				:spellchecking="false"
 				:autocomplete="autoCompleteAllowed ? 'username' : 'off'"
 				required
-				:error="userNameInputLengthIs255"
+				:error="userNameError"
 				:helper-text="userInputHelperText"
 				data-login-form-input-user
 				@change="updateUsername" />
@@ -241,6 +241,10 @@ export default {
 				|| this.throttleDelay > 5000
 		},
 
+		userNameError() {
+			return this.isError || this.userNameInputLengthIs255
+		},
+
 		errorLabel() {
 			if (this.invalidPassword) {
 				return t('core', 'Wrong login or password.')
diff --git a/core/src/tests/components/Login/LoginForm.spec.ts b/core/src/tests/components/Login/LoginForm.spec.ts
index b471c9bdf81df..9c6299bd2d40f 100644
--- a/core/src/tests/components/Login/LoginForm.spec.ts
+++ b/core/src/tests/components/Login/LoginForm.spec.ts
@@ -66,6 +66,18 @@ describe('core: LoginForm', () => {
 		expect(input.value).toBe('test-user')
 	})
 
+	it('marks username field as error when login credentials are invalid', () => {
+		const page = render(LoginForm, {
+			props: {
+				errors: ['invalidpassword'],
+				username: 'wrong-user',
+			},
+		})
+
+		const input = page.getByRole('textbox', { name: /Account name or email/ })
+		expect(input.closest('.input-field--error')).not.toBeNull()
+	})
+
 	describe('', () => {
 		beforeAll(() => {
 			vi.useFakeTimers()
diff --git a/tests/playwright/e2e/login/login.spec.ts b/tests/playwright/e2e/login/login.spec.ts
index 6101e80f2e009..be003950a907f 100644
--- a/tests/playwright/e2e/login/login.spec.ts
+++ b/tests/playwright/e2e/login/login.spec.ts
@@ -45,24 +45,26 @@ test.describe('Login', () => {
 		await expect(page).toHaveURL(/apps\/dashboard(\/|$)/)
 	})
 
-	test('wrong password shows error and marks password field invalid', async ({ page, user }) => {
+	test('wrong password shows error and marks both fields invalid', async ({ page, user }) => {
 		const loginPage = new LoginPage(page)
 		await loginPage.goto()
 		await loginPage.login(user.userId, `${user.password}--wrong`)
 
 		await expect(page).toHaveURL(/\/login/)
 		await expect(page.getByText(/Wrong login or password/i)).toBeVisible()
-		await expect(loginPage.passwordInput().and(page.locator(':invalid'))).toHaveCount(1)
+		await expect(page.locator('.input-field--error').filter({ has: loginPage.usernameInput() })).toBeVisible()
+		await expect(page.locator('.input-field--error').filter({ has: loginPage.passwordInput() })).toBeVisible()
 	})
 
-	test('wrong account name shows error and marks password field invalid', async ({ page, user }) => {
+	test('wrong account name shows error and marks both fields invalid', async ({ page, user }) => {
 		const loginPage = new LoginPage(page)
 		await loginPage.goto()
 		await loginPage.login(`${user.userId}--wrong`, user.password)
 
 		await expect(page).toHaveURL(/\/login/)
 		await expect(page.getByText(/Wrong login or password/i)).toBeVisible()
-		await expect(loginPage.passwordInput().and(page.locator(':invalid'))).toHaveCount(1)
+		await expect(page.locator('.input-field--error').filter({ has: loginPage.usernameInput() })).toBeVisible()
+		await expect(page.locator('.input-field--error').filter({ has: loginPage.passwordInput() })).toBeVisible()
 	})
 
 	test('disabled account shows disabled error', async ({ page, disabledUser }) => {
@@ -72,7 +74,8 @@ test.describe('Login', () => {
 
 		await expect(page).toHaveURL(/\/login/)
 		await expect(page.getByText(/Account.*disabled/i)).toBeVisible()
-		await expect(loginPage.passwordInput().and(page.locator(':invalid'))).toHaveCount(1)
+		await expect(page.locator('.input-field--error').filter({ has: loginPage.usernameInput() })).toBeVisible()
+		await expect(page.locator('.input-field--error').filter({ has: loginPage.passwordInput() })).toBeVisible()
 	})
 
 	test('logout redirects to the login page', async ({ page, context, user }) => {