diff --git a/src/protocols/bootloader.ts b/src/protocols/bootloader.ts
index b9e8f37c..700f4ea9 100644
--- a/src/protocols/bootloader.ts
+++ b/src/protocols/bootloader.ts
@@ -77,6 +77,20 @@ export enum ProtectionLevel {
     Level2 = 0x02,
 }
 
+/**
+ * Protocol error. Thrown e.g. when there is a malformed message.
+ */
+export class ProtocolError extends Error {
+    /**
+     * Creates a new ProtocolError.
+     * @param message The error message
+     * @param data The bytecodes that caused the error
+     */
+    constructor(message: string, public data: DataView) {
+        super(message);
+    }
+}
+
 /**
  * Creates a new message to erase the flash memory.
  */
@@ -192,11 +206,20 @@ export function parseErrorResponse(msg: DataView): Command {
     assert(msg.getUint8(0) === 5, 'unexpected length');
     // Error responses are ordered differently compared to command responses.
     if (msg.getUint8(2) !== ErrorBytecode) {
-        throw Error('expecting error');
+        throw new ProtocolError(
+            `expecting error bytecode 0x05 but got 0x${msg
+                .getUint8(2)
+                .toString(16)
+                .padStart(2, '0')}`,
+            msg,
+        );
     }
     if (msg.getUint8(4) !== ErrorCode.UnknownCommand) {
         // "command not recognized" is only possible error code
-        throw Error('unexpected error code');
+        throw new ProtocolError(
+            `unknown error code: 0x${msg.getUint8(4).toString(16).padStart(2, '0')}`,
+            msg,
+        );
     }
     const command = msg.getUint8(3);
     return command;
diff --git a/src/sagas/bootloader.test.ts b/src/sagas/bootloader.test.ts
index e516ee26..f8132b16 100644
--- a/src/sagas/bootloader.test.ts
+++ b/src/sagas/bootloader.test.ts
@@ -7,6 +7,7 @@ import {
     BootloaderRequestActionType,
     checksumRequest,
     checksumResponse,
+    didError,
     didReceive,
     didRequest,
     didSend,
@@ -25,7 +26,13 @@ import {
     stateRequest,
     stateResponse,
 } from '../actions/bootloader';
-import { Command, HubType, ProtectionLevel, Result } from '../protocols/bootloader';
+import {
+    Command,
+    HubType,
+    ProtectionLevel,
+    ProtocolError,
+    Result,
+} from '../protocols/bootloader';
 import { createCountFunc } from '../utils/iter';
 import bootloader from './bootloader';
 
@@ -271,4 +278,70 @@ describe('message decoder', () => {
         await task.toPromise();
         expect(dispatched[0]).toEqual(expected);
     });
+
+    test.each([
+        [
+            'bad error bytecode',
+            [
+                0x05, // length
+                0x00, // unused (hub id)
+                0x04, // **invalid message type**
+                0x77, // get flash state command
+                0x05, // command not recognized
+            ],
+            didError(
+                new ProtocolError(
+                    'expecting error bytecode 0x05 but got 0x04',
+                    new DataView(new Uint8Array().buffer),
+                ),
+            ),
+        ],
+        [
+            'unknown error code',
+            [
+                0x05, // length
+                0x00, // unused (hub id)
+                0x05, // flash loader error message
+                0x77, // get flash state command
+                0x04, // **invalid error code**
+            ],
+            didError(
+                new ProtocolError(
+                    'unknown error code: 0x04',
+                    new DataView(new Uint8Array().buffer),
+                ),
+            ),
+        ],
+        [
+            'unknown response',
+            [
+                0x00, // **bad command**
+                0x01, // **junk**
+                0x02, // **junk**
+                0x03, // **junk**
+                0x04, // **junk**
+            ],
+            didError(
+                new ProtocolError(
+                    'unknown bootloader response type: 0x00',
+                    new DataView(new Uint8Array().buffer),
+                ),
+            ),
+        ],
+    ])('protocol error', async (_n, message, expected) => {
+        const response = new Uint8Array(message);
+        const channel = stdChannel();
+        const dispatched = new Array<Action>();
+        const task = runSaga(
+            {
+                channel,
+                dispatch: (action: Action) => dispatched.push(action),
+            },
+            bootloader,
+        );
+        channel.put(didReceive(new DataView(response.buffer)));
+        task.cancel();
+        await task.toPromise();
+        expect(dispatched[0]).toEqual(expected);
+    });
 });
diff --git a/src/sagas/bootloader.ts b/src/sagas/bootloader.ts
index 3541b35a..a9cbd1cc 100644
--- a/src/sagas/bootloader.ts
+++ b/src/sagas/bootloader.ts
@@ -42,6 +42,7 @@ import {
     checksumRequest,
     checksumResponse,
     connect,
+    didError,
     didRequest,
     disconnectRequest,
     eraseRequest,
@@ -65,6 +66,7 @@ import {
     ErrorBytecode,
     HubType,
     MaxProgramFlashSize,
+    ProtocolError,
     createDisconnectRequest,
     createEraseFlashRequest,
     createGetChecksumRequest,
@@ -184,11 +186,15 @@ function* decodeResponse(action: BootloaderConnectionDidReceiveAction): Generato
                 yield put(errorResponse(parseErrorResponse(action.data)));
                 break;
             default:
-                throw new Error(`Unknown bootloader response action ${action}`);
+                throw new ProtocolError(
+                    `unknown bootloader response type: 0x${responseType
+                        .toString(16)
+                        .padStart(2, '0')}`,
+                    action.data,
+                );
         }
     } catch (err) {
-        // TODO: dispatch an error action
-        console.error(`Error decoding message: ${err}`);
+        yield put(didError(err));
     }
 }
 
diff --git a/tsconfig.json b/tsconfig.json
index eed8da05..17f28503 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,6 +1,6 @@
 {
     "compilerOptions": {
-        "target": "es5",
+        "target": "es2018",
         "lib": ["dom", "dom.iterable", "esnext"],
         "allowJs": true,
         "skipLibCheck": true,