diff --git a/web/account/traditional-login-form.react.js b/web/account/traditional-login-form.react.js
index 3690681c4..33ec3ace8 100644
--- a/web/account/traditional-login-form.react.js
+++ b/web/account/traditional-login-form.react.js
@@ -1,266 +1,272 @@
 // @flow
 
 import invariant from 'invariant';
 import * as React from 'react';
 
 import {
   useLegacyLogIn,
   legacyLogInActionTypes,
 } from 'lib/actions/user-actions.js';
 import { useModalContext } from 'lib/components/modal-provider.react.js';
 import { usePasswordLogIn } from 'lib/hooks/login-hooks.js';
 import { legacyLogInExtraInfoSelector } from 'lib/selectors/account-selectors.js';
 import { createLoadingStatusSelector } from 'lib/selectors/loading-selectors.js';
 import {
   oldValidUsernameRegex,
   validEmailRegex,
 } from 'lib/shared/account-utils.js';
 import type {
   LegacyLogInExtraInfo,
   LegacyLogInStartingPayload,
 } from 'lib/types/account-types.js';
 import { logInActionSources } from 'lib/types/account-types.js';
 import { getMessageForException } from 'lib/utils/errors.js';
 import { useDispatchActionPromise } from 'lib/utils/redux-promise-utils.js';
 import { usingCommServicesAccessToken } from 'lib/utils/services-utils.js';
 
 import HeaderSeparator from './header-separator.react.js';
 import css from './log-in-form.css';
 import PasswordInput from './password-input.react.js';
 import Button from '../components/button.react.js';
 import { olmAPI } from '../crypto/olm-api.js';
 import LoadingIndicator from '../loading-indicator.react.js';
 import Input from '../modals/input.react.js';
 import { useSelector } from '../redux/redux-utils.js';
 import { getShortVersionUnsupportedError } from '../utils/version-utils.js';
 
 const loadingStatusSelector = createLoadingStatusSelector(
   legacyLogInActionTypes,
 );
 function TraditionalLoginForm(): React.Node {
   const legacyAuthInProgress = useSelector(loadingStatusSelector) === 'loading';
   const [identityAuthInProgress, setIdentityAuthInProgress] =
     React.useState(false);
   const inputDisabled = legacyAuthInProgress || identityAuthInProgress;
 
   const legacyLoginExtraInfo = useSelector(legacyLogInExtraInfoSelector);
   const callLegacyLogIn = useLegacyLogIn();
 
   const dispatchActionPromise = useDispatchActionPromise();
   const modalContext = useModalContext();
 
   const usernameInputRef = React.useRef<?HTMLInputElement>();
   React.useEffect(() => {
     usernameInputRef.current?.focus();
   }, []);
 
   const [username, setUsername] = React.useState<string>('');
   const onUsernameChange = React.useCallback(
     (e: SyntheticEvent<HTMLInputElement>) => {
       invariant(e.target instanceof HTMLInputElement, 'target not input');
       setUsername(e.target.value);
     },
     [],
   );
 
   const onUsernameBlur = React.useCallback(() => {
     setUsername(untrimmedUsername => untrimmedUsername.trim());
   }, []);
 
   const [password, setPassword] = React.useState<string>('');
   const onPasswordChange = React.useCallback(
     (e: SyntheticEvent<HTMLInputElement>) => {
       invariant(e.target instanceof HTMLInputElement, 'target not input');
       setPassword(e.target.value);
     },
     [],
   );
 
   const [errorMessage, setErrorMessage] = React.useState<string>('');
 
   const legacyLogInAction = React.useCallback(
     async (extraInfo: LegacyLogInExtraInfo) => {
       await olmAPI.initializeCryptoAccount();
       const userPublicKey = await olmAPI.getUserPublicKey();
       try {
         const result = await callLegacyLogIn({
           ...extraInfo,
           username,
           password,
           authActionSource: logInActionSources.logInFromWebForm,
           signedIdentityKeysBlob: {
             payload: userPublicKey.blobPayload,
             signature: userPublicKey.signature,
           },
         });
         modalContext.popModal();
         return result;
       } catch (e) {
         setUsername('');
         setPassword('');
         const messageForException = getMessageForException(e);
         if (messageForException === 'invalid_credentials') {
           setErrorMessage('incorrect username or password');
         } else if (messageForException === 'client_version_unsupported') {
           setErrorMessage(getShortVersionUnsupportedError());
         } else {
           setErrorMessage('unknown error');
         }
         usernameInputRef.current?.focus();
         throw e;
       }
     },
     [callLegacyLogIn, modalContext, password, username],
   );
 
   const callIdentityPasswordLogIn = usePasswordLogIn();
 
   const identityPasswordLogInAction = React.useCallback(async () => {
     if (identityAuthInProgress) {
       return;
     }
     setIdentityAuthInProgress(true);
     try {
       await callIdentityPasswordLogIn(username, password);
       modalContext.popModal();
     } catch (e) {
       setUsername('');
       setPassword('');
       const messageForException = getMessageForException(e);
       if (
         messageForException === 'user_not_found' ||
         messageForException === 'login_failed'
       ) {
         setErrorMessage('incorrect username or password');
       } else if (
         messageForException === 'client_version_unsupported' ||
         messageForException === 'unsupported_version'
       ) {
         setErrorMessage(getShortVersionUnsupportedError());
+      } else if (
+        messageForException === 'need_keyserver_message_to_claim_username'
+      ) {
+        // We don't want to let users claim their reserved usernames from web
+        // because we won't be able to establish a primary device for them.
+        setErrorMessage('please log in from a mobile device then retry');
       } else {
         setErrorMessage('unknown error');
       }
       usernameInputRef.current?.focus();
     } finally {
       setIdentityAuthInProgress(false);
     }
   }, [
     identityAuthInProgress,
     callIdentityPasswordLogIn,
     modalContext,
     password,
     username,
   ]);
 
   const onSubmit = React.useCallback(
     (event: SyntheticEvent<HTMLElement>) => {
       event.preventDefault();
 
       if (username.search(validEmailRegex) > -1) {
         setUsername('');
         setErrorMessage('usernames only, not emails');
         usernameInputRef.current?.focus();
         return;
       } else if (username.search(oldValidUsernameRegex) === -1) {
         setUsername('');
         setErrorMessage('alphanumeric usernames only');
         usernameInputRef.current?.focus();
         return;
       } else if (password === '') {
         setErrorMessage('password is empty');
         usernameInputRef.current?.focus();
         return;
       }
       if (usingCommServicesAccessToken) {
         void identityPasswordLogInAction();
       } else {
         void dispatchActionPromise(
           legacyLogInActionTypes,
           legacyLogInAction(legacyLoginExtraInfo),
           undefined,
           ({
             calendarQuery: legacyLoginExtraInfo.calendarQuery,
           }: LegacyLogInStartingPayload),
         );
       }
     },
     [
       dispatchActionPromise,
       identityPasswordLogInAction,
       legacyLogInAction,
       legacyLoginExtraInfo,
       username,
       password,
     ],
   );
 
   const loadingIndicatorClassName = inputDisabled
     ? css.loadingIndicator
     : css.hiddenLoadingIndicator;
   const buttonTextClassName = inputDisabled
     ? css.invisibleButtonText
     : undefined;
   const loginButtonContent = React.useMemo(
     () => (
       <>
         <div className={loadingIndicatorClassName}>
           <LoadingIndicator status="loading" />
         </div>
         <div className={buttonTextClassName}>Sign in</div>
       </>
     ),
     [loadingIndicatorClassName, buttonTextClassName],
   );
 
   const signInButtonColor = React.useMemo(
     () => ({ backgroundColor: '#6A20E3' }),
     [],
   );
 
   return (
     <form method="POST">
       <div>
         <h4>Sign in to Comm</h4>
         <HeaderSeparator />
         <div className={css.form_title}>Username</div>
         <div className={css.form_content}>
           <Input
             className={css.input}
             type="text"
             placeholder="Username"
             value={username}
             onChange={onUsernameChange}
             onBlur={onUsernameBlur}
             ref={usernameInputRef}
             disabled={inputDisabled}
           />
         </div>
       </div>
       <div>
         <div className={css.form_title}>Password</div>
         <div className={css.form_content}>
           <PasswordInput
             className={css.input}
             value={password}
             onChange={onPasswordChange}
             disabled={inputDisabled}
           />
         </div>
       </div>
       <div className={css.form_footer}>
         <Button
           variant="filled"
           type="submit"
           disabled={inputDisabled}
           onClick={onSubmit}
           buttonColor={signInButtonColor}
         >
           {loginButtonContent}
         </Button>
         <div className={css.modal_form_error}>{errorMessage}</div>
       </div>
     </form>
   );
 }
 
 export default TraditionalLoginForm;