diff --git a/.babelrc b/.babelrc
index 6e6720bbf11..0ea353e6d0a 100644
--- a/.babelrc
+++ b/.babelrc
@@ -5,16 +5,16 @@
             "@babel/preset-env",
             {
                 "targets": {
-                    "node": 10
+                    "node": 18
                 },
-                "modules": "commonjs"
+                "modules": "commonjs",
+                "include": ["@babel/plugin-proposal-class-properties"]
             }
         ],
-        "@babel/preset-typescript"
+        ["@babel/preset-typescript", { "allowDeclareFields": true }]
     ],
     "plugins": [
         "@babel/plugin-proposal-numeric-separator",
-        "@babel/plugin-proposal-class-properties",
         "@babel/plugin-proposal-object-rest-spread",
         "@babel/plugin-syntax-dynamic-import",
         "@babel/plugin-transform-runtime"
diff --git a/src/crypto/algorithms/base.ts b/src/crypto/algorithms/base.ts
index 647300948bd..c7d4ccdf150 100644
--- a/src/crypto/algorithms/base.ts
+++ b/src/crypto/algorithms/base.ts
@@ -19,10 +19,10 @@ limitations under the License.
  */
 
 import type { IMegolmSessionData } from "../../@types/crypto";
+import type { IContent, MatrixEvent, RoomMember } from "../../matrix";
 import { MatrixClient } from "../../client";
 import { Room } from "../../models/room";
 import { OlmDevice } from "../OlmDevice";
-import { IContent, MatrixEvent, RoomMember } from "../../matrix";
 import { Crypto, IEncryptedContent, IEventDecryptionResult, IncomingRoomKeyRequest } from "..";
 import { DeviceInfo } from "../deviceinfo";
 import { IRoomEncryption } from "../RoomList";
diff --git a/src/crypto/algorithms/megolm.ts b/src/crypto/algorithms/megolm.ts
index 061e169e39b..2b3f48bbe96 100644
--- a/src/crypto/algorithms/megolm.ts
+++ b/src/crypto/algorithms/megolm.ts
@@ -245,7 +245,7 @@ export class MegolmEncryption extends EncryptionAlgorithm {
         cancel: () => void;
     };
 
-    protected readonly roomId: string;
+    protected declare readonly roomId: string;
     private readonly prefixedLogger: PrefixedLogger;
 
     public constructor(params: IParams & Required<Pick<IParams, "roomId">>) {
@@ -1290,7 +1290,7 @@ export class MegolmDecryption extends DecryptionAlgorithm {
     // this gets stubbed out by the unit tests.
     private olmlib = olmlib;
 
-    protected readonly roomId: string;
+    protected declare readonly roomId: string;
     private readonly prefixedLogger: PrefixedLogger;
 
     public constructor(params: DecryptionClassParams<IParams & Required<Pick<IParams, "roomId">>>) {
diff --git a/src/crypto/index.ts b/src/crypto/index.ts
index ab588afce9f..1475e68b3fd 100644
--- a/src/crypto/index.ts
+++ b/src/crypto/index.ts
@@ -38,7 +38,7 @@ import { SecretStorage as LegacySecretStorage } from "./SecretStorage";
 import { CrossSigningKey, ICreateSecretStorageOpts, IEncryptedEventInfo, IRecoveryKey } from "./api";
 import { OutgoingRoomKeyRequestManager } from "./OutgoingRoomKeyRequestManager";
 import { IndexedDBCryptoStore } from "./store/indexeddb-crypto-store";
-import { VerificationBase } from "./verification/Base";
+import type { VerificationBase } from "./verification/Base";
 import { ReciprocateQRCode, SCAN_QR_CODE_METHOD, SHOW_QR_CODE_METHOD } from "./verification/QRCode";
 import { SAS as SASVerification } from "./verification/SAS";
 import { keyFromPassphrase } from "./key_passphrase";
diff --git a/src/crypto/verification/request/Channel.ts b/src/crypto/verification/request/Channel.ts
index 48415f977e1..1ab08331fbc 100644
--- a/src/crypto/verification/request/Channel.ts
+++ b/src/crypto/verification/request/Channel.ts
@@ -14,8 +14,8 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { MatrixEvent } from "../../../models/event";
-import { VerificationRequest } from "./VerificationRequest";
+import type { MatrixEvent } from "../../../models/event";
+import type { VerificationRequest } from "./VerificationRequest";
 
 export interface IVerificationChannel {
     request?: VerificationRequest;
diff --git a/src/models/room-member.ts b/src/models/room-member.ts
index e8fcfa60620..8312fc82d56 100644
--- a/src/models/room-member.ts
+++ b/src/models/room-member.ts
@@ -14,10 +14,10 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import type { MatrixEvent } from "./event";
 import { getHttpUriForMxc } from "../content-repo";
 import { removeDirectionOverrideChars, removeHiddenChars } from "../utils";
 import { User } from "./user";
-import { MatrixEvent } from "./event";
 import { RoomState } from "./room-state";
 import { logger } from "../logger";
 import { TypedEventEmitter } from "./typed-event-emitter";
diff --git a/src/models/user.ts b/src/models/user.ts
index 054a17438f2..79c9fb0023e 100644
--- a/src/models/user.ts
+++ b/src/models/user.ts
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { MatrixEvent } from "./event";
+import type { MatrixEvent } from "./event";
 import { TypedEventEmitter } from "./typed-event-emitter";
 
 export enum UserEvent {
diff --git a/src/utils.ts b/src/utils.ts
index 1dba236c9c5..a40c8e7722d 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -22,7 +22,7 @@ import unhomoglyph from "unhomoglyph";
 import promiseRetry from "p-retry";
 import { Optional } from "matrix-events-sdk";
 
-import { IEvent, MatrixEvent } from "./models/event";
+import type { IEvent, MatrixEvent } from "./models/event";
 import { M_TIMESTAMP } from "./@types/location";
 import { ReceiptType } from "./@types/read_receipts";
 
diff --git a/tsconfig.json b/tsconfig.json
index 13fed86c47b..6dc306e67a2 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,5 +1,6 @@
 {
     "compilerOptions": {
+        "useDefineForClassFields": true,
         "target": "es2016",
         "experimentalDecorators": true,
         "esModuleInterop": true,