diff --git a/src/actions/ble.ts b/src/actions/ble.ts
index 9e791308..40151489 100644
--- a/src/actions/ble.ts
+++ b/src/actions/ble.ts
@@ -1,5 +1,9 @@
 import { Action } from 'redux';
 import { ThunkAction } from 'redux-thunk';
+import {
+    PolyfillBluetoothRemoteGATTCharacteristic,
+    polyfillBluetoothRemoteGATTCharacteristic,
+} from '../utils/web-bluetooth';
 import * as notification from './notification';
 
 const pybricksServiceUUID = 'c5f50001-8280-46da-89f4-6d8051e4aeef';
@@ -11,7 +15,7 @@ const bleNusCharTXUUID = '6e400003-b5a3-f393-e0a9-e50e24dcca9e';
 const bleNusMaxSize = 20;
 
 let device: BluetoothDevice | undefined;
-let rxChar: BluetoothRemoteGATTCharacteristic | undefined;
+let rxChar: PolyfillBluetoothRemoteGATTCharacteristic | undefined;
 
 export enum BLEConnectActionType {
     /**
@@ -120,7 +124,9 @@ export function connect(): BLEThunkAction {
         const server = await device.gatt.connect();
         try {
             const service = await server.getPrimaryService(bleNusServiceUUID);
-            rxChar = await service.getCharacteristic(bleNusCharRXUUID);
+            rxChar = polyfillBluetoothRemoteGATTCharacteristic(
+                await service.getCharacteristic(bleNusCharRXUUID),
+            );
             const txChar = await service.getCharacteristic(bleNusCharTXUUID);
             txChar.addEventListener('characteristicvaluechanged', () => {
                 if (!txChar.value) {
@@ -150,7 +156,7 @@ export function write(value: ArrayBuffer): BLEThunkAction {
     return async function (): Promise<void> {
         // TODO: do we need to dispatch any Action<>s here?
         for (let i = 0; i < value.byteLength; i += bleNusMaxSize) {
-            await rxChar?.writeValue(value.slice(i, i + bleNusMaxSize));
+            await rxChar?.writeValueWithoutResponse(value.slice(i, i + bleNusMaxSize));
         }
     };
 }
diff --git a/src/services/bootloader.ts b/src/services/bootloader.ts
index 3cf994d5..4d6c760b 100644
--- a/src/services/bootloader.ts
+++ b/src/services/bootloader.ts
@@ -10,10 +10,14 @@ import {
     didSend,
 } from '../actions/bootloader';
 import { CharacteristicUUID, ServiceUUID } from '../protocols/bootloader';
+import {
+    PolyfillBluetoothRemoteGATTCharacteristic,
+    polyfillBluetoothRemoteGATTCharacteristic,
+} from '../utils/web-bluetooth';
 import { combineServices } from '.';
 
 let device: BluetoothDevice | undefined;
-let char: BluetoothRemoteGATTCharacteristic | undefined;
+let char: PolyfillBluetoothRemoteGATTCharacteristic | undefined;
 
 async function connect(action: Action, dispatch: Dispatch): Promise<void> {
     if (action.type !== BootloaderConnectionActionType.Connect) {
@@ -55,7 +59,9 @@ async function connect(action: Action, dispatch: Dispatch): Promise<void> {
         const server = await device.gatt.connect();
         try {
             const service = await server.getPrimaryService(ServiceUUID);
-            char = await service.getCharacteristic(CharacteristicUUID);
+            char = polyfillBluetoothRemoteGATTCharacteristic(
+                await service.getCharacteristic(CharacteristicUUID),
+            );
             char.addEventListener('characteristicvaluechanged', () => {
                 if (!char || !char.value) {
                     return;
@@ -82,16 +88,11 @@ async function send(action: Action, dispatch: Dispatch): Promise<void> {
             throw Error('Not connected');
         }
         const sendAction = action as BootloaderConnectionSendAction;
-        // Fall back to legacy WebBluetooth writeValue if new methods are not
-        // available.
-        const writeValue = sendAction.withResponse
-            ? // eslint-disable-next-line @typescript-eslint/ban-ts-ignore
-              // @ts-ignore
-              char.writeValueWithResponse || char.writeValue
-            : // eslint-disable-next-line @typescript-eslint/ban-ts-ignore
-              // @ts-ignore
-              char.writeValueWithoutResponse || char.writeValue;
-        await writeValue(sendAction.data);
+        if (sendAction.withResponse) {
+            await char.writeValueWithResponse(sendAction.data);
+        } else {
+            await char.writeValueWithoutResponse(sendAction.data);
+        }
         dispatch(didSend());
     } catch (err) {
         dispatch(didSend(err));
diff --git a/src/utils/web-bluetooth.ts b/src/utils/web-bluetooth.ts
new file mode 100644
index 00000000..66f5191c
--- /dev/null
+++ b/src/utils/web-bluetooth.ts
@@ -0,0 +1,27 @@
+/**
+ * Current definition of BluetoothRemoteGATTCharacteristic doesn't include
+ * new Web Bluetooth APIs.
+ */
+export interface PolyfillBluetoothRemoteGATTCharacteristic
+    extends BluetoothRemoteGATTCharacteristic {
+    writeValueWithResponse(value: BufferSource): Promise<void>;
+    writeValueWithoutResponse(value: BufferSource): Promise<void>;
+}
+
+/**
+ * Fills in writeValueWithResponse and writeValueWithoutResponse for backward
+ * compatibility.
+ * @param char a remote GATT characteristic object
+ */
+export function polyfillBluetoothRemoteGATTCharacteristic(
+    char: BluetoothRemoteGATTCharacteristic,
+): PolyfillBluetoothRemoteGATTCharacteristic {
+    const polyfill = (char as unknown) as PolyfillBluetoothRemoteGATTCharacteristic;
+    if (!polyfill.writeValueWithResponse) {
+        polyfill.writeValueWithResponse = char.writeValue;
+    }
+    if (!polyfill.writeValueWithoutResponse) {
+        polyfill.writeValueWithoutResponse = char.writeValue;
+    }
+    return polyfill;
+}