diff --git a/components/ui/UsernameInput.tsx b/components/ui/UsernameInput.tsx
new file mode 100644
index 00000000..31d2ba03
--- /dev/null
+++ b/components/ui/UsernameInput.tsx
@@ -0,0 +1,17 @@
+import React from "react";
+
+export const UsernameInput = React.forwardRef( (props, ref) => (
+  // todo, check if username is already taken here?
+  <div>
+    <label htmlFor="username" className="block text-sm font-medium text-gray-700">
+      Username
+    </label>
+    <div className="mt-1 rounded-md shadow-sm flex">
+      <span className="bg-gray-50 border border-r-0 border-gray-300 rounded-l-md px-3 inline-flex items-center text-gray-500 sm:text-sm">
+        {typeof window !== "undefined" && window.location.hostname}/
+      </span>
+      <input ref={ref} type="text" name="username" id="username" autoComplete="username" required defaultValue={props.defaultValue}
+             className="focus:ring-blue-500 focus:border-blue-500 flex-grow block w-full min-w-0 rounded-none rounded-r-md sm:text-sm border-gray-300"/>
+    </div>
+  </div>
+));
\ No newline at end of file
diff --git a/components/ui/alerts/Error.tsx b/components/ui/alerts/Error.tsx
new file mode 100644
index 00000000..8cc23998
--- /dev/null
+++ b/components/ui/alerts/Error.tsx
@@ -0,0 +1,22 @@
+
+import { XCircleIcon } from '@heroicons/react/solid'
+
+export default function ErrorAlert(props) {
+  return (
+    <div className="rounded-md bg-red-50 p-4">
+      <div className="flex">
+        <div className="flex-shrink-0">
+          <XCircleIcon className="h-5 w-5 text-red-400" aria-hidden="true" />
+        </div>
+        <div className="ml-3">
+          <h3 className="text-sm font-medium text-red-800">Something went wrong</h3>
+          <div className="text-sm text-red-700">
+            <p>
+              {props.message}
+            </p>
+          </div>
+        </div>
+      </div>
+    </div>
+  )
+}
\ No newline at end of file
diff --git a/pages/api/user/profile.ts b/pages/api/user/profile.ts
index f1b2e18d..fb47f5d2 100644
--- a/pages/api/user/profile.ts
+++ b/pages/api/user/profile.ts
@@ -3,46 +3,58 @@ import { getSession } from 'next-auth/client';
 import prisma from '../../../lib/prisma';
 
 export default async function handler(req: NextApiRequest, res: NextApiResponse) {
-    const session = await getSession({req: req});
+  const session = await getSession({req: req});
 
-    if (!session) {
-        res.status(401).json({message: "Not authenticated"});
-        return;
+  if (!session) {
+      res.status(401).json({message: "Not authenticated"});
+      return;
+  }
+
+  // Get user
+  const user = await prisma.user.findUnique({
+    where: {
+      email: session.user.email,
+    },
+    select: {
+      id: true,
+      password: true
     }
+  });
 
-    // Get user
-    const user = await prisma.user.findFirst({
-        where: {
-            email: session.user.email,
-        },
-        select: {
-            id: true,
-            password: true
-        }
+  if (!user) { res.status(404).json({message: 'User not found'}); return; }
+
+  const username = req.body.username;
+  // username is changed: username is optional but it is necessary to be unique, enforce here
+  if (username !== user.username) {
+    const userConflict = await prisma.user.findFirst({
+      where: {
+        username,
+      }
     });
+    if (userConflict) {
+      return res.status(409).json({ message: 'Username already taken' });
+    }
+  }
 
-    if (!user) { res.status(404).json({message: 'User not found'}); return; }
+  const name = req.body.name;
+  const description = req.body.description;
+  const avatar = req.body.avatar;
+  const timeZone = req.body.timeZone;
+  const weekStart = req.body.weekStart;
 
-    const username = req.body.username;
-    const name = req.body.name;
-    const description = req.body.description;
-    const avatar = req.body.avatar;
-    const timeZone = req.body.timeZone;
-    const weekStart = req.body.weekStart;
+  const updateUser = await prisma.user.update({
+    where: {
+      id: user.id,
+    },
+    data: {
+      username,
+      name,
+      avatar,
+      bio: description,
+      timeZone: timeZone,
+      weekStart: weekStart,
+    },
+  });
 
-    const updateUser = await prisma.user.update({
-        where: {
-          id: user.id,
-        },
-        data: {
-          username,
-          name,
-          avatar,
-          bio: description,
-          timeZone: timeZone,
-          weekStart: weekStart,
-        },
-    });
-
-    res.status(200).json({message: 'Profile updated successfully'});
+  return res.status(200).json({message: 'Profile updated successfully'});
 }
\ No newline at end of file
diff --git a/pages/settings/profile.tsx b/pages/settings/profile.tsx
index d0a11294..20787966 100644
--- a/pages/settings/profile.tsx
+++ b/pages/settings/profile.tsx
@@ -9,6 +9,8 @@ import SettingsShell from '../../components/Settings';
 import Avatar from '../../components/Avatar';
 import { signIn, useSession, getSession } from 'next-auth/client';
 import TimezoneSelect from 'react-timezone-select';
+import {UsernameInput} from "../../components/ui/UsernameInput";
+import ErrorAlert from "../../components/ui/alerts/Error";
 
 export default function Settings(props) {
     const [ session, loading ] = useSession();
@@ -22,12 +24,22 @@ export default function Settings(props) {
     const [ selectedTimeZone, setSelectedTimeZone ] = useState({ value: props.user.timeZone });
     const [ selectedWeekStartDay, setSelectedWeekStartDay ] = useState(props.user.weekStart || 'Sunday');
 
+    const [ hasErrors, setHasErrors ] = useState(false);
+    const [ errorMessage, setErrorMessage ] = useState('');
+
     if (loading) {
         return <p className="text-gray-400">Loading...</p>;
     }
 
     const closeSuccessModal = () => { setSuccessModalOpen(false); }
 
+    const handleError = async (resp) => {
+      if (!resp.ok) {
+        const error = await resp.json();
+        throw new Error(error.message);
+      }
+    }
+
     async function updateProfileHandler(event) {
         event.preventDefault();
 
@@ -46,10 +58,10 @@ export default function Settings(props) {
             headers: {
                 'Content-Type': 'application/json'
             }
+        }).then(handleError).then( () => setSuccessModalOpen(true) ).catch( (err) => {
+          setHasErrors(true);
+          setErrorMessage(err.message);
         });
-
-        router.replace(router.asPath);
-        setSuccessModalOpen(true);
     }
 
     return(
@@ -60,6 +72,7 @@ export default function Settings(props) {
             </Head>
             <SettingsShell>
                 <form className="divide-y divide-gray-200 lg:col-span-9" onSubmit={updateProfileHandler}>
+                    {hasErrors && <ErrorAlert message={errorMessage} />}
                     <div className="py-6 px-4 sm:p-6 lg:pb-8">
                         <div>
                             <h2 className="text-lg leading-6 font-medium text-gray-900">Profile</h2>
@@ -72,15 +85,7 @@ export default function Settings(props) {
                             <div className="flex-grow space-y-6">
                                 <div className="flex">
                                     <div className="w-1/2 mr-2">
-                                        <label htmlFor="username" className="block text-sm font-medium text-gray-700">
-                                            Username
-                                        </label>
-                                        <div className="mt-1 rounded-md shadow-sm flex">
-                                            <span className="bg-gray-50 border border-r-0 border-gray-300 rounded-l-md px-3 inline-flex items-center text-gray-500 sm:text-sm">
-                                                {window.location.hostname}/
-                                            </span>
-                                            <input ref={usernameRef} type="text" name="username" id="username" autoComplete="username" required className="focus:ring-blue-500 focus:border-blue-500 flex-grow block w-full min-w-0 rounded-none rounded-r-md sm:text-sm border-gray-300" defaultValue={props.user.username} />
-                                        </div>
+                                        <UsernameInput ref={usernameRef} defaultValue={props.user.username} />
                                     </div>
                                     <div className="w-1/2 ml-2">
                                         <label htmlFor="name" className="block text-sm font-medium text-gray-700">Full name</label>