diff --git a/src/ConferenceCallManagerHooks.jsx b/src/ConferenceCallManagerHooks.jsx
index 7a5a815..13e2251 100644
--- a/src/ConferenceCallManagerHooks.jsx
+++ b/src/ConferenceCallManagerHooks.jsx
@@ -28,7 +28,6 @@ import {
   GroupCallType,
 } from "matrix-js-sdk/src/browser-index";
 import { useHistory } from "react-router-dom";
-import { randomString } from "matrix-js-sdk/src/randomstring";
 
 const ClientContext = createContext();
 
@@ -432,7 +431,7 @@ export function useClient() {
   return useContext(ClientContext);
 }
 
-function roomAliasFromRoomName(roomName) {
+export function roomAliasFromRoomName(roomName) {
   return roomName
     .trim()
     .replace(/\s/g, "-")
@@ -485,41 +484,6 @@ export async function createRoom(client, name) {
   return room_alias || room_id;
 }
 
-export function useCreateRoom() {
-  const { register, client } = useClient();
-  const [creatingRoom, setCreatingRoom] = useState(false);
-  const [createRoomError, setCreateRoomError] = useState();
-
-  const onCreateRoom = useCallback(
-    (roomName, userName) => {
-      async function onCreateRoom(roomName, userName) {
-        let _client = client;
-
-        if (!_client) {
-          _client = await register(userName, randomString(16), true);
-        }
-
-        return await createRoom(_client, roomName);
-      }
-
-      setCreateRoomError(undefined);
-      setCreatingRoom(true);
-
-      return onCreateRoom(roomName, userName).catch((error) => {
-        setCreateRoomError(error);
-        setCreatingRoom(false);
-      });
-    },
-    [register, client]
-  );
-
-  return {
-    creatingRoom,
-    createRoomError,
-    createRoom: onCreateRoom,
-  };
-}
-
 export function useLoadGroupCall(client, roomId, viaServers) {
   const [state, setState] = useState({
     loading: true,
diff --git a/src/Home.jsx b/src/Home.jsx
index 1ac5f2e..9af93c7 100644
--- a/src/Home.jsx
+++ b/src/Home.jsx
@@ -14,13 +14,14 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React, { useCallback } from "react";
+import React, { useCallback, useState } from "react";
 import { useHistory, Link } from "react-router-dom";
 import {
   useClient,
   useGroupCallRooms,
   usePublicRooms,
-  useCreateRoom,
+  createRoom,
+  roomAliasFromRoomName,
 } from "./ConferenceCallManagerHooks";
 import { Header, HeaderLogo, LeftNav, RightNav } from "./Header";
 import styles from "./Home.module.css";
@@ -30,6 +31,9 @@ import { Button } from "./button";
 import { CallList } from "./CallList";
 import classNames from "classnames";
 import { ErrorView, LoadingView } from "./FullScreenView";
+import { useModalTriggerState } from "./Modal";
+import { randomString } from "matrix-js-sdk/src/randomstring";
+import { JoinExistingCallModal } from "./JoinExistingCallModal";
 
 export function Home() {
   const {
@@ -39,10 +43,14 @@ export function Home() {
     loading,
     error,
     client,
+    register,
   } = useClient();
 
   const history = useHistory();
-  const { createRoomError, creatingRoom, createRoom } = useCreateRoom();
+  const [creatingRoom, setCreatingRoom] = useState(false);
+  const [createRoomError, setCreateRoomError] = useState();
+  const { modalState, modalProps } = useModalTriggerState();
+  const [existingRoomId, setExistingRoomId] = useState();
 
   const onCreateRoom = useCallback(
     (e) => {
@@ -51,13 +59,36 @@ export function Home() {
       const roomName = data.get("roomName");
       const userName = data.get("userName");
 
-      createRoom(roomName, userName).then((roomIdOrAlias) => {
+      async function onCreateRoom() {
+        let _client = client;
+
+        if (!_client) {
+          _client = await register(userName, randomString(16), true);
+        }
+
+        const roomIdOrAlias = await createRoom(_client, roomName);
+
         if (roomIdOrAlias) {
           history.push(`/room/${roomIdOrAlias}`);
         }
+      }
+
+      setCreateRoomError(undefined);
+      setCreatingRoom(true);
+
+      return onCreateRoom().catch((error) => {
+        if (error.errcode === "M_ROOM_IN_USE") {
+          setExistingRoomId(roomAliasFromRoomName(roomName));
+          setCreateRoomError(undefined);
+          modalState.open();
+        } else {
+          setCreateRoomError(error);
+        }
+
+        setCreatingRoom(false);
       });
     },
-    [history]
+    [client, history, register]
   );
 
   const onJoinRoom = useCallback(
@@ -70,30 +101,39 @@ export function Home() {
     [history]
   );
 
+  const onJoinExistingRoom = useCallback(() => {
+    history.push(`/${existingRoomId}`);
+  }, [history, existingRoomId]);
+
   if (loading) {
     return <LoadingView />;
-  } else if (error || createRoomError) {
-    return <ErrorView error={error || createRoomError} />;
-  } else if (!isAuthenticated || isGuest) {
-    return (
-      <UnregisteredView
-        onCreateRoom={onCreateRoom}
-        createRoomError={createRoomError}
-        creatingRoom={creatingRoom}
-        onJoinRoom={onJoinRoom}
-      />
-    );
+  } else if (error) {
+    return <ErrorView error={error} />;
   } else {
     return (
-      <RegisteredView
-        client={client}
-        isPasswordlessUser={isPasswordlessUser}
-        isGuest={isGuest}
-        onCreateRoom={onCreateRoom}
-        createRoomError={createRoomError}
-        creatingRoom={creatingRoom}
-        onJoinRoom={onJoinRoom}
-      />
+      <>
+        {!isAuthenticated || isGuest ? (
+          <UnregisteredView
+            onCreateRoom={onCreateRoom}
+            createRoomError={createRoomError}
+            creatingRoom={creatingRoom}
+            onJoinRoom={onJoinRoom}
+          />
+        ) : (
+          <RegisteredView
+            client={client}
+            isPasswordlessUser={isPasswordlessUser}
+            isGuest={isGuest}
+            onCreateRoom={onCreateRoom}
+            createRoomError={createRoomError}
+            creatingRoom={creatingRoom}
+            onJoinRoom={onJoinRoom}
+          />
+        )}
+        {modalState.isOpen && (
+          <JoinExistingCallModal onJoin={onJoinExistingRoom} {...modalProps} />
+        )}
+      </>
     );
   }
 }
diff --git a/src/JoinExistingCallModal.jsx b/src/JoinExistingCallModal.jsx
new file mode 100644
index 0000000..20a0a18
--- /dev/null
+++ b/src/JoinExistingCallModal.jsx
@@ -0,0 +1,19 @@
+import React from "react";
+import { Modal, ModalContent } from "./Modal";
+import { Button } from "./button";
+import { FieldRow } from "./Input";
+import styles from "./JoinExistingCallModal.module.css";
+
+export function JoinExistingCallModal({ onJoin, ...rest }) {
+  return (
+    <Modal title="Join existing call?" isDismissable {...rest}>
+      <ModalContent>
+        <p>This call already exists, would you like to join?</p>
+        <FieldRow rightAlign className={styles.buttons}>
+          <Button onPress={rest.onClose}>No</Button>
+          <Button onPress={onJoin}>Yes, join call</Button>
+        </FieldRow>
+      </ModalContent>
+    </Modal>
+  );
+}
diff --git a/src/JoinExistingCallModal.module.css b/src/JoinExistingCallModal.module.css
new file mode 100644
index 0000000..86bfe1b
--- /dev/null
+++ b/src/JoinExistingCallModal.module.css
@@ -0,0 +1,3 @@
+.buttons {
+  margin-bottom: 0;
+}
diff --git a/src/randomstring.js b/src/randomstring.js
deleted file mode 100644
index 85a5bec..0000000
--- a/src/randomstring.js
+++ /dev/null
@@ -1,42 +0,0 @@
-/*
-Copyright 2018 New Vector Ltd
-Copyright 2019 The Matrix.org Foundation C.I.C.
-
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
-*/
-
-const LOWERCASE = "abcdefghijklmnopqrstuvwxyz";
-const UPPERCASE = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
-const DIGITS = "0123456789";
-
-export function randomString(len) {
-  return randomStringFrom(len, UPPERCASE + LOWERCASE + DIGITS);
-}
-
-export function randomLowercaseString(len) {
-  return randomStringFrom(len, LOWERCASE);
-}
-
-export function randomUppercaseString(len) {
-  return randomStringFrom(len, UPPERCASE);
-}
-
-function randomStringFrom(len, chars) {
-  let ret = "";
-
-  for (let i = 0; i < len; ++i) {
-    ret += chars.charAt(Math.floor(Math.random() * chars.length));
-  }
-
-  return ret;
-}