diff --git a/src/ScalarMessaging.ts b/src/ScalarMessaging.ts
index e500c34828..0c103aa17d 100644
--- a/src/ScalarMessaging.ts
+++ b/src/ScalarMessaging.ts
@@ -626,7 +626,8 @@ async function setBotPower(
             success: true,
         });
     } catch (err) {
-        sendError(event, err instanceof Error ? err.message : _t("Failed to send request."), err);
+        const error = err instanceof Error ? err : undefined;
+        sendError(event, error?.message ?? _t("Failed to send request."), error);
     }
 }
 
diff --git a/src/SlashCommands.tsx b/src/SlashCommands.tsx
index ce9d6cd187..a044dedfaa 100644
--- a/src/SlashCommands.tsx
+++ b/src/SlashCommands.tsx
@@ -1105,7 +1105,7 @@ export const Commands = [
             try {
                 cli.forceDiscardSession(roomId);
             } catch (e) {
-                return reject(e.message);
+                return reject(e instanceof Error ? e.message : e);
             }
             return success();
         },
@@ -1134,7 +1134,7 @@ export const Commands = [
                     }),
                 );
             } catch (e) {
-                return reject(e.message);
+                return reject(e instanceof Error ? e.message : e);
             }
         },
         category: CommandCategories.advanced,
diff --git a/src/async-components/views/dialogs/security/CreateSecretStorageDialog.tsx b/src/async-components/views/dialogs/security/CreateSecretStorageDialog.tsx
index 8f57c07e1a..bf39565a4f 100644
--- a/src/async-components/views/dialogs/security/CreateSecretStorageDialog.tsx
+++ b/src/async-components/views/dialogs/security/CreateSecretStorageDialog.tsx
@@ -20,10 +20,11 @@ import FileSaver from "file-saver";
 import { logger } from "matrix-js-sdk/src/logger";
 import { IKeyBackupInfo } from "matrix-js-sdk/src/crypto/keybackup";
 import { TrustInfo } from "matrix-js-sdk/src/crypto/backup";
-import { CrossSigningKeys, MatrixError, UIAFlow } from "matrix-js-sdk/src/matrix";
+import { CrossSigningKeys, IAuthDict, MatrixError, UIAFlow } from "matrix-js-sdk/src/matrix";
 import { IRecoveryKey } from "matrix-js-sdk/src/crypto/api";
 import { CryptoEvent } from "matrix-js-sdk/src/crypto";
 import classNames from "classnames";
+import { UIAResponse } from "matrix-js-sdk/src/@types/uia";
 
 import { MatrixClientPeg } from "../../../../MatrixClientPeg";
 import { _t, _td } from "../../../../languageHandler";
@@ -90,7 +91,7 @@ interface IState {
     accountPasswordCorrect: boolean | null;
     canSkip: boolean;
     passPhraseKeySelected: string;
-    error?: string;
+    error?: boolean;
 }
 
 /*
@@ -279,7 +280,9 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
         });
     };
 
-    private doBootstrapUIAuth = async (makeRequest: (authData: any) => Promise<{}>): Promise<void> => {
+    private doBootstrapUIAuth = async (
+        makeRequest: (authData: IAuthDict) => Promise<UIAResponse<void>>,
+    ): Promise<void> => {
         if (this.state.canUploadKeysWithPasswordOnly && this.state.accountPassword) {
             await makeRequest({
                 type: "m.login.password",
@@ -385,7 +388,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
                     phase: Phase.Migrate,
                 });
             } else {
-                this.setState({ error: e });
+                this.setState({ error: true });
             }
             logger.error("Error bootstrapping secret storage", e);
         }
diff --git a/src/components/structures/auth/Registration.tsx b/src/components/structures/auth/Registration.tsx
index 5492b4f039..eeca4a9719 100644
--- a/src/components/structures/auth/Registration.tsx
+++ b/src/components/structures/auth/Registration.tsx
@@ -246,11 +246,11 @@ export default class Registration extends React.Component<IProps, IState> {
             }
         } catch (e) {
             if (serverConfig !== this.latestServerConfig) return; // discard, serverConfig changed from under us
-            if (e.httpStatus === 401) {
+            if (e instanceof MatrixError && e.httpStatus === 401) {
                 this.setState({
                     flows: e.data.flows,
                 });
-            } else if (e.httpStatus === 403 || e.errcode === "M_FORBIDDEN") {
+            } else if (e instanceof MatrixError && (e.httpStatus === 403 || e.errcode === "M_FORBIDDEN")) {
                 // Check for 403 or M_FORBIDDEN, Synapse used to send 403 M_UNKNOWN but now sends 403 M_FORBIDDEN.
                 // At this point registration is pretty much disabled, but before we do that let's
                 // quickly check to see if the server supports SSO instead. If it does, we'll send
diff --git a/src/components/views/dialogs/ChangelogDialog.tsx b/src/components/views/dialogs/ChangelogDialog.tsx
index 8321cc40f4..56b5758c62 100644
--- a/src/components/views/dialogs/ChangelogDialog.tsx
+++ b/src/components/views/dialogs/ChangelogDialog.tsx
@@ -60,7 +60,7 @@ export default class ChangelogDialog extends React.Component<IProps, State> {
             const body = await res.json();
             this.setState({ [repo]: body.commits });
         } catch (err) {
-            this.setState({ [repo]: err.message });
+            this.setState({ [repo]: err instanceof Error ? err.message : _t("Unknown error") });
         }
     }
 
diff --git a/src/components/views/dialogs/LogoutDialog.tsx b/src/components/views/dialogs/LogoutDialog.tsx
index bf92719c19..9830cf5992 100644
--- a/src/components/views/dialogs/LogoutDialog.tsx
+++ b/src/components/views/dialogs/LogoutDialog.tsx
@@ -39,7 +39,6 @@ interface IState {
     shouldLoadBackupStatus: boolean;
     loading: boolean;
     backupInfo: IKeyBackupInfo | null;
-    error?: string;
 }
 
 export default class LogoutDialog extends React.Component<IProps, IState> {
@@ -75,7 +74,6 @@ export default class LogoutDialog extends React.Component<IProps, IState> {
             logger.log("Unable to fetch key backup status", e);
             this.setState({
                 loading: false,
-                error: e,
             });
         }
     }
diff --git a/src/components/views/dialogs/ReportEventDialog.tsx b/src/components/views/dialogs/ReportEventDialog.tsx
index ecf7c856e0..f5912131b5 100644
--- a/src/components/views/dialogs/ReportEventDialog.tsx
+++ b/src/components/views/dialogs/ReportEventDialog.tsx
@@ -272,7 +272,7 @@ export default class ReportEventDialog extends React.Component<IProps, IState> {
             logger.error(e);
             this.setState({
                 busy: false,
-                err: e.message,
+                err: e instanceof Error ? e.message : String(e),
             });
         }
     };
diff --git a/src/components/views/dialogs/security/CreateCrossSigningDialog.tsx b/src/components/views/dialogs/security/CreateCrossSigningDialog.tsx
index 7a6412c8ed..d27e7aec04 100644
--- a/src/components/views/dialogs/security/CreateCrossSigningDialog.tsx
+++ b/src/components/views/dialogs/security/CreateCrossSigningDialog.tsx
@@ -18,7 +18,8 @@ limitations under the License.
 import React from "react";
 import { CrossSigningKeys } from "matrix-js-sdk/src/client";
 import { logger } from "matrix-js-sdk/src/logger";
-import { UIAFlow } from "matrix-js-sdk/src/matrix";
+import { AuthDict, MatrixError, UIAFlow } from "matrix-js-sdk/src/matrix";
+import { UIAResponse } from "matrix-js-sdk/src/@types/uia";
 
 import { MatrixClientPeg } from "../../../../MatrixClientPeg";
 import { _t } from "../../../../languageHandler";
@@ -79,7 +80,7 @@ export default class CreateCrossSigningDialog extends React.PureComponent<IProps
             // no keys which would be a no-op.
             logger.log("uploadDeviceSigningKeys unexpectedly succeeded without UI auth!");
         } catch (error) {
-            if (!error.data || !error.data.flows) {
+            if (!(error instanceof MatrixError) || !error.data || !error.data.flows) {
                 logger.log("uploadDeviceSigningKeys advertised no flows!");
                 return;
             }
@@ -92,7 +93,9 @@ export default class CreateCrossSigningDialog extends React.PureComponent<IProps
         }
     }
 
-    private doBootstrapUIAuth = async (makeRequest: (authData: any) => Promise<{}>): Promise<void> => {
+    private doBootstrapUIAuth = async (
+        makeRequest: (authData: AuthDict) => Promise<UIAResponse<void>>,
+    ): Promise<void> => {
         if (this.state.canUploadKeysWithPasswordOnly && this.state.accountPassword) {
             await makeRequest({
                 type: "m.login.password",
diff --git a/src/components/views/dialogs/security/RestoreKeyBackupDialog.tsx b/src/components/views/dialogs/security/RestoreKeyBackupDialog.tsx
index d4eb3a0bd7..7ec4caa429 100644
--- a/src/components/views/dialogs/security/RestoreKeyBackupDialog.tsx
+++ b/src/components/views/dialogs/security/RestoreKeyBackupDialog.tsx
@@ -55,7 +55,7 @@ interface IState {
     backupInfo: IKeyBackupInfo | null;
     backupKeyStored: Record<string, ISecretStorageKeyInfo> | null;
     loading: boolean;
-    loadError: string | null;
+    loadError: boolean | null;
     restoreError: {
         errcode: string;
     } | null;
@@ -66,7 +66,7 @@ interface IState {
     passPhrase: string;
     restoreType: RestoreType | null;
     progress: {
-        stage: ProgressState;
+        stage: ProgressState | string;
         total?: number;
         successes?: number;
         failures?: number;
@@ -304,7 +304,7 @@ export default class RestoreKeyBackupDialog extends React.PureComponent<IProps,
         } catch (e) {
             logger.log("Error loading backup status", e);
             this.setState({
-                loadError: e,
+                loadError: true,
                 loading: false,
             });
         }
diff --git a/src/components/views/elements/LazyRenderList.tsx b/src/components/views/elements/LazyRenderList.tsx
index 802e60ca19..355d673404 100644
--- a/src/components/views/elements/LazyRenderList.tsx
+++ b/src/components/views/elements/LazyRenderList.tsx
@@ -92,7 +92,7 @@ export default class LazyRenderList<T = any> extends React.Component<IProps<T>,
         this.state = LazyRenderList.getDerivedStateFromProps(props, {} as IState) as IState;
     }
 
-    public static getDerivedStateFromProps(props: IProps<unknown>, state: IState): Partial<IState> | null {
+    public static getDerivedStateFromProps<T>(props: IProps<T>, state: IState): Partial<IState> | null {
         const range = LazyRenderList.getVisibleRangeFromProps(props);
         const intersectRange = range.expand(props.overflowMargin);
         const renderRange = range.expand(props.overflowItems);
@@ -105,7 +105,7 @@ export default class LazyRenderList<T = any> extends React.Component<IProps<T>,
         return null;
     }
 
-    private static getVisibleRangeFromProps(props: IProps<unknown>): ItemRange {
+    private static getVisibleRangeFromProps<T>(props: IProps<T>): ItemRange {
         const { items, itemHeight, scrollTop, height } = props;
         const length = items ? items.length : 0;
         const topCount = Math.min(Math.max(0, Math.floor(scrollTop / itemHeight)), length);
diff --git a/src/components/views/elements/RoomAliasField.tsx b/src/components/views/elements/RoomAliasField.tsx
index 10549d79db..6590bba783 100644
--- a/src/components/views/elements/RoomAliasField.tsx
+++ b/src/components/views/elements/RoomAliasField.tsx
@@ -15,6 +15,7 @@ limitations under the License.
 */
 
 import React, { createRef, KeyboardEventHandler } from "react";
+import { MatrixError } from "matrix-js-sdk/src/matrix";
 
 import { _t } from "../../../languageHandler";
 import withValidation, { IFieldState, IValidationResult } from "./Validation";
@@ -209,7 +210,7 @@ export default class RoomAliasField extends React.PureComponent<IProps, IState>
                               // any server error code will do,
                               // either it M_NOT_FOUND or the alias is invalid somehow,
                               // in which case we don't want to show the invalid message
-                              return !!err.errcode;
+                              return err instanceof MatrixError;
                           }
                       },
                       valid: () => _t("This address is available to use"),
diff --git a/src/components/views/settings/devices/deleteDevices.tsx b/src/components/views/settings/devices/deleteDevices.tsx
index 3fa042864a..b1f527187d 100644
--- a/src/components/views/settings/devices/deleteDevices.tsx
+++ b/src/components/views/settings/devices/deleteDevices.tsx
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { MatrixClient } from "matrix-js-sdk/src/matrix";
+import { MatrixClient, MatrixError } from "matrix-js-sdk/src/matrix";
 import { IAuthDict, IAuthData } from "matrix-js-sdk/src/interactive-auth";
 
 import { _t } from "../../../../languageHandler";
@@ -42,7 +42,7 @@ export const deleteDevicesWithInteractiveAuth = async (
         // no interactive auth needed
         onFinished(true, undefined);
     } catch (error) {
-        if (error.httpStatus !== 401 || !error.data?.flows) {
+        if (!(error instanceof MatrixError) || error.httpStatus !== 401 || !error.data?.flows) {
             // doesn't look like an interactive-auth failure
             throw error;
         }
@@ -73,7 +73,7 @@ export const deleteDevicesWithInteractiveAuth = async (
         Modal.createDialog(InteractiveAuthDialog, {
             title: _t("Authentication"),
             matrixClient: matrixClient,
-            authData: error.data,
+            authData: error.data as IAuthData,
             onFinished,
             makeRequest: makeDeleteRequest(matrixClient, deviceIds),
             aestheticsForStagePhases: {
diff --git a/src/components/views/toasts/VerificationRequestToast.tsx b/src/components/views/toasts/VerificationRequestToast.tsx
index 37c1683d81..2476c7ce44 100644
--- a/src/components/views/toasts/VerificationRequestToast.tsx
+++ b/src/components/views/toasts/VerificationRequestToast.tsx
@@ -147,7 +147,7 @@ export default class VerificationRequestToast extends React.PureComponent<IProps
             }
             await request.accept();
         } catch (err) {
-            logger.error(err.message);
+            logger.error("Failed to accept verification request", err);
         }
     };
 
diff --git a/src/hooks/useLocalStorageState.ts b/src/hooks/useLocalStorageState.ts
index 76d167d5ee..c2a710c221 100644
--- a/src/hooks/useLocalStorageState.ts
+++ b/src/hooks/useLocalStorageState.ts
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { Dispatch, SetStateAction, useCallback, useEffect, useState } from "react";
+import { Dispatch, useCallback, useEffect, useState } from "react";
 
 const getValue = <T>(key: string, initialValue: T): T => {
     try {
@@ -26,7 +26,7 @@ const getValue = <T>(key: string, initialValue: T): T => {
 };
 
 // Hook behaving like useState but persisting the value to localStorage. Returns same as useState
-export const useLocalStorageState = <T>(key: string, initialValue: T): [T, Dispatch<SetStateAction<T>>] => {
+export const useLocalStorageState = <T>(key: string, initialValue: T): [T, Dispatch<T>] => {
     const lsKey = "mx_" + key;
 
     const [value, setValue] = useState<T>(getValue(lsKey, initialValue));
@@ -35,7 +35,7 @@ export const useLocalStorageState = <T>(key: string, initialValue: T): [T, Dispa
         setValue(getValue(lsKey, initialValue));
     }, [lsKey, initialValue]);
 
-    const _setValue: Dispatch<SetStateAction<T>> = useCallback(
+    const _setValue: Dispatch<T> = useCallback(
         (v: T) => {
             window.localStorage.setItem(lsKey, JSON.stringify(v));
             setValue(v);
diff --git a/src/hooks/useStateCallback.ts b/src/hooks/useStateCallback.ts
index 39863666c6..ab73f26520 100644
--- a/src/hooks/useStateCallback.ts
+++ b/src/hooks/useStateCallback.ts
@@ -14,11 +14,11 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { Dispatch, SetStateAction, useState } from "react";
+import { Dispatch, useState } from "react";
 
 // Hook to simplify interactions with a store-backed state values
 // Returns value and method to change the state value
-export const useStateCallback = <T>(initialValue: T, callback: (v: T) => void): [T, Dispatch<SetStateAction<T>>] => {
+export const useStateCallback = <T>(initialValue: T, callback: (v: T) => void): [T, Dispatch<T>] => {
     const [value, setValue] = useState(initialValue);
     const interceptSetValue = (newVal: T): void => {
         setValue(newVal);
diff --git a/src/i18n/strings/en_EN.json b/src/i18n/strings/en_EN.json
index d2e280ff13..5c51a0f7fc 100644
--- a/src/i18n/strings/en_EN.json
+++ b/src/i18n/strings/en_EN.json
@@ -2765,6 +2765,7 @@
     "Remove %(count)s messages|one": "Remove 1 message",
     "Can't start voice message": "Can't start voice message",
     "You can't start a voice message as you are currently recording a live broadcast. Please end your live broadcast in order to start recording a voice message.": "You can't start a voice message as you are currently recording a live broadcast. Please end your live broadcast in order to start recording a voice message.",
+    "Unknown error": "Unknown error",
     "Unable to load commit detail: %(msg)s": "Unable to load commit detail: %(msg)s",
     "Unavailable": "Unavailable",
     "Changelog": "Changelog",
@@ -3469,7 +3470,6 @@
     "You don't have permission": "You don't have permission",
     "This room is suggested as a good one to join": "This room is suggested as a good one to join",
     "Suggested": "Suggested",
-    "Unknown error": "Unknown error",
     "Select a room below first": "Select a room below first",
     "Mark as not suggested": "Mark as not suggested",
     "Mark as suggested": "Mark as suggested",
diff --git a/src/settings/SettingsStore.ts b/src/settings/SettingsStore.ts
index 7169494f4c..457908d858 100644
--- a/src/settings/SettingsStore.ts
+++ b/src/settings/SettingsStore.ts
@@ -666,7 +666,9 @@ export default class SettingsStore {
                     logger.log(`---     ${handlerName}@${roomId || "<no_room>"} = ${JSON.stringify(value)}`);
                 } catch (e) {
                     logger.log(
-                        `---     ${handler.constructor.name}@${roomId || "<no_room>"} THREW ERROR: ${e.message}`,
+                        `---     ${handler.constructor.name}@${roomId || "<no_room>"} THREW ERROR: ${
+                            e instanceof Error ? e.message : e
+                        }`,
                     );
                     logger.error(e);
                 }
@@ -676,7 +678,11 @@ export default class SettingsStore {
                         const value = handler.getValue(settingName, null);
                         logger.log(`---     ${handlerName}@<no_room> = ${JSON.stringify(value)}`);
                     } catch (e) {
-                        logger.log(`---     ${handler.constructor.name}@<no_room> THREW ERROR: ${e.message}`);
+                        logger.log(
+                            `---     ${handler.constructor.name}@<no_room> THREW ERROR: ${
+                                e instanceof Error ? e.message : e
+                            }`,
+                        );
                         logger.error(e);
                     }
                 }
@@ -689,7 +695,11 @@ export default class SettingsStore {
                 const value = SettingsStore.getValue(settingName, roomId);
                 logger.log(`---     SettingsStore#generic@${roomId || "<no_room>"}  = ${JSON.stringify(value)}`);
             } catch (e) {
-                logger.log(`---     SettingsStore#generic@${roomId || "<no_room>"} THREW ERROR: ${e.message}`);
+                logger.log(
+                    `---     SettingsStore#generic@${roomId || "<no_room>"} THREW ERROR: ${
+                        e instanceof Error ? e.message : e
+                    }`,
+                );
                 logger.error(e);
             }
 
@@ -698,7 +708,9 @@ export default class SettingsStore {
                     const value = SettingsStore.getValue(settingName, null);
                     logger.log(`---     SettingsStore#generic@<no_room>  = ${JSON.stringify(value)}`);
                 } catch (e) {
-                    logger.log(`---     SettingsStore#generic@$<no_room> THREW ERROR: ${e.message}`);
+                    logger.log(
+                        `---     SettingsStore#generic@$<no_room> THREW ERROR: ${e instanceof Error ? e.message : e}`,
+                    );
                     logger.error(e);
                 }
             }
@@ -708,7 +720,11 @@ export default class SettingsStore {
                     const value = SettingsStore.getValueAt(level, settingName, roomId);
                     logger.log(`---     SettingsStore#${level}@${roomId || "<no_room>"} = ${JSON.stringify(value)}`);
                 } catch (e) {
-                    logger.log(`---     SettingsStore#${level}@${roomId || "<no_room>"} THREW ERROR: ${e.message}`);
+                    logger.log(
+                        `---     SettingsStore#${level}@${roomId || "<no_room>"} THREW ERROR: ${
+                            e instanceof Error ? e.message : e
+                        }`,
+                    );
                     logger.error(e);
                 }
 
@@ -717,7 +733,11 @@ export default class SettingsStore {
                         const value = SettingsStore.getValueAt(level, settingName, null);
                         logger.log(`---     SettingsStore#${level}@<no_room> = ${JSON.stringify(value)}`);
                     } catch (e) {
-                        logger.log(`---     SettingsStore#${level}@$<no_room> THREW ERROR: ${e.message}`);
+                        logger.log(
+                            `---     SettingsStore#${level}@$<no_room> THREW ERROR: ${
+                                e instanceof Error ? e.message : e
+                            }`,
+                        );
                         logger.error(e);
                     }
                 }
diff --git a/src/utils/MultiInviter.ts b/src/utils/MultiInviter.ts
index 1cff080a63..31ca6f87b5 100644
--- a/src/utils/MultiInviter.ts
+++ b/src/utils/MultiInviter.ts
@@ -178,7 +178,7 @@ export default class MultiInviter {
                 } catch (err) {
                     // The error handling during the invitation process covers any API.
                     // Some errors must to me mapped from profile API errors to more specific ones to avoid collisions.
-                    switch (err.errcode) {
+                    switch (err instanceof MatrixError ? err.errcode : err) {
                         case "M_FORBIDDEN":
                             throw new MatrixError({ errcode: "M_PROFILE_UNDISCLOSED" });
                         case "M_NOT_FOUND":
diff --git a/src/utils/UserInteractiveAuth.ts b/src/utils/UserInteractiveAuth.ts
index 2eed476c3c..e78f88cbce 100644
--- a/src/utils/UserInteractiveAuth.ts
+++ b/src/utils/UserInteractiveAuth.ts
@@ -14,13 +14,13 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { IAuthDict } from "matrix-js-sdk/src/interactive-auth";
+import { AuthDict } from "matrix-js-sdk/src/interactive-auth";
 import { UIAResponse } from "matrix-js-sdk/src/@types/uia";
 
 import Modal from "../Modal";
 import InteractiveAuthDialog, { InteractiveAuthDialogProps } from "../components/views/dialogs/InteractiveAuthDialog";
 
-type FunctionWithUIA<R, A> = (auth?: IAuthDict | null, ...args: A[]) => Promise<UIAResponse<R>>;
+type FunctionWithUIA<R, A> = (auth?: AuthDict, ...args: A[]) => Promise<UIAResponse<R>>;
 
 export function wrapRequestWithDialog<R, A = any>(
     requestFunction: FunctionWithUIA<R, A>,
@@ -29,7 +29,7 @@ export function wrapRequestWithDialog<R, A = any>(
     return async function (...args): Promise<R> {
         return new Promise((resolve, reject) => {
             const boundFunction = requestFunction.bind(opts.matrixClient) as FunctionWithUIA<R, A>;
-            boundFunction(null, ...args)
+            boundFunction(undefined, ...args)
                 .then((res) => resolve(res as R))
                 .catch((error) => {
                     if (error.httpStatus !== 401 || !error.data?.flows) {
@@ -40,7 +40,7 @@ export function wrapRequestWithDialog<R, A = any>(
                     Modal.createDialog(InteractiveAuthDialog, {
                         ...opts,
                         authData: error.data,
-                        makeRequest: (authData: IAuthDict | null) => boundFunction(authData, ...args),
+                        makeRequest: (authData: AuthDict) => boundFunction(authData, ...args),
                         onFinished: (success, result) => {
                             if (success) {
                                 resolve(result as R);
diff --git a/test/components/structures/auth/Registration-test.tsx b/test/components/structures/auth/Registration-test.tsx
index 3f6f44db7e..e72ffc58b9 100644
--- a/test/components/structures/auth/Registration-test.tsx
+++ b/test/components/structures/auth/Registration-test.tsx
@@ -17,8 +17,7 @@ limitations under the License.
 
 import React from "react";
 import { fireEvent, render, screen, waitForElementToBeRemoved } from "@testing-library/react";
-import { createClient, MatrixClient } from "matrix-js-sdk/src/matrix";
-import { MatrixError } from "matrix-js-sdk/src/http-api/errors";
+import { createClient, MatrixClient, MatrixError } from "matrix-js-sdk/src/matrix";
 import { mocked } from "jest-mock";
 import fetchMock from "fetch-mock-jest";
 
@@ -26,7 +25,10 @@ import SdkConfig, { DEFAULTS } from "../../../../src/SdkConfig";
 import { mkServerConfig, mockPlatformPeg, unmockPlatformPeg } from "../../../test-utils";
 import Registration from "../../../../src/components/structures/auth/Registration";
 
-jest.mock("matrix-js-sdk/src/matrix");
+jest.mock("matrix-js-sdk/src/matrix", () => ({
+    ...jest.requireActual("matrix-js-sdk/src/matrix"),
+    createClient: jest.fn(),
+}));
 jest.useFakeTimers();
 
 describe("Registration", function () {
diff --git a/test/components/views/dialogs/CreateRoomDialog-test.tsx b/test/components/views/dialogs/CreateRoomDialog-test.tsx
index d312f0eaa0..f675efd023 100644
--- a/test/components/views/dialogs/CreateRoomDialog-test.tsx
+++ b/test/components/views/dialogs/CreateRoomDialog-test.tsx
@@ -16,7 +16,7 @@ limitations under the License.
 
 import React from "react";
 import { fireEvent, render, screen, within } from "@testing-library/react";
-import { Preset, Visibility } from "matrix-js-sdk/src/matrix";
+import { MatrixError, Preset, Visibility } from "matrix-js-sdk/src/matrix";
 
 import CreateRoomDialog from "../../../../src/components/views/dialogs/CreateRoomDialog";
 import { flushPromises, getMockClientWithEventEmitter, mockClientMethodsUser } from "../../../test-utils";
@@ -29,7 +29,7 @@ describe("<CreateRoomDialog />", () => {
         getClientWellKnown: jest.fn(),
         doesServerForceEncryptionForPreset: jest.fn(),
         // make every alias available
-        getRoomIdForAlias: jest.fn().mockRejectedValue({ errcode: "M_NOT_FOUND" }),
+        getRoomIdForAlias: jest.fn().mockRejectedValue(new MatrixError({ errcode: "M_NOT_FOUND" })),
     });
 
     const getE2eeEnableToggleInputElement = () => screen.getByLabelText("Enable end-to-end encryption");
diff --git a/test/components/views/dialogs/InteractiveAuthDialog-test.tsx b/test/components/views/dialogs/InteractiveAuthDialog-test.tsx
index 1fce8783e8..76a6607ed2 100644
--- a/test/components/views/dialogs/InteractiveAuthDialog-test.tsx
+++ b/test/components/views/dialogs/InteractiveAuthDialog-test.tsx
@@ -131,7 +131,7 @@ describe("InteractiveAuthDialog", function () {
             const successfulResult = { test: 1 };
             const makeRequest = jest
                 .fn()
-                .mockRejectedValueOnce(new MatrixError({ data: { flows: [{ stages: ["m.login.sso"] }] } }, 401))
+                .mockRejectedValueOnce(new MatrixError({ flows: [{ stages: ["m.login.sso"] }] }, 401))
                 .mockResolvedValue(successfulResult);
 
             mockClient.credentials = { userId: "@user:id" };
diff --git a/test/components/views/settings/devices/deleteDevices-test.tsx b/test/components/views/settings/devices/deleteDevices-test.tsx
index bdd0c5a8c2..ca748d9896 100644
--- a/test/components/views/settings/devices/deleteDevices-test.tsx
+++ b/test/components/views/settings/devices/deleteDevices-test.tsx
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { UIAFlow } from "matrix-js-sdk/src/matrix";
+import { MatrixError, UIAFlow } from "matrix-js-sdk/src/matrix";
 
 import { deleteDevicesWithInteractiveAuth } from "../../../../../src/components/views/settings/devices/deleteDevices";
 import Modal from "../../../../../src/Modal";
@@ -30,7 +30,7 @@ describe("deleteDevices()", () => {
 
     const modalSpy = jest.spyOn(Modal, "createDialog") as jest.SpyInstance;
 
-    const interactiveAuthError = { httpStatus: 401, data: { flows: [] as UIAFlow[] } };
+    const interactiveAuthError = new MatrixError({ flows: [] as UIAFlow[] }, 401);
 
     beforeEach(() => {
         jest.clearAllMocks();
diff --git a/test/components/views/settings/tabs/user/SessionManagerTab-test.tsx b/test/components/views/settings/tabs/user/SessionManagerTab-test.tsx
index f2e34d37e6..3de4eff002 100644
--- a/test/components/views/settings/tabs/user/SessionManagerTab-test.tsx
+++ b/test/components/views/settings/tabs/user/SessionManagerTab-test.tsx
@@ -31,6 +31,7 @@ import {
     UNSTABLE_MSC3882_CAPABILITY,
     CryptoApi,
     DeviceVerificationStatus,
+    MatrixError,
 } from "matrix-js-sdk/src/matrix";
 import { mocked } from "jest-mock";
 
@@ -722,10 +723,12 @@ describe("<SessionManagerTab />", () => {
         });
 
         describe("other devices", () => {
-            const interactiveAuthError = {
-                httpStatus: 401,
-                data: { flows: [{ stages: ["m.login.password"] }] },
-            };
+            const interactiveAuthError = new MatrixError(
+                {
+                    flows: [{ stages: ["m.login.password"] }],
+                },
+                401,
+            );
 
             beforeEach(() => {
                 mockClient.deleteMultipleDevices.mockReset();
diff --git a/test/utils/MultiInviter-test.ts b/test/utils/MultiInviter-test.ts
index 2c25cd5e3a..4e63407119 100644
--- a/test/utils/MultiInviter-test.ts
+++ b/test/utils/MultiInviter-test.ts
@@ -32,8 +32,8 @@ const MXID3 = "@user3:server";
 
 const MXID_PROFILE_STATES: Record<string, Promise<any>> = {
     [MXID1]: Promise.resolve({}),
-    [MXID2]: Promise.reject({ errcode: "M_FORBIDDEN" }),
-    [MXID3]: Promise.reject({ errcode: "M_NOT_FOUND" }),
+    [MXID2]: Promise.reject(new MatrixError({ errcode: "M_FORBIDDEN" })),
+    [MXID3]: Promise.reject(new MatrixError({ errcode: "M_NOT_FOUND" })),
 };
 
 jest.mock("../../src/Modal", () => ({