diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5a6c40e6..59842dbd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,12 @@
 
 ## [Unreleased]
 
+### Fixed
+- Fix flashing firmware on Android [support#403].
+
+### Changed
+- Checksum is now validated as firmware flash progresses instead of just at the
+  end [support#433].
 
 ## [1.1.0-beta.3] - 2021-07-20
 
@@ -46,13 +52,15 @@
 Prerelease changes are documented at [support#48].
 
 
-<!-- let's try to keep this list sorted -->
+<!-- let's try to keep this list sorted alphabetically -->
 [issue#470]: https://github.com/pybricks/pybricks-code/issues/470
 [issue#471]: https://github.com/pybricks/pybricks-code/issues/471
 [issue#472]: https://github.com/pybricks/pybricks-code/issues/472
 [support#48]: https://github.com/pybricks/support/issues/48
 [support#375]: https://github.com/pybricks/support/issues/375
 [support#378]: https://github.com/pybricks/support/issues/378
+[support#403]: https://github.com/pybricks/support/issues/403
+[support#433]: https://github.com/pybricks/support/issues/433
 [v3.0.0]: https://github.com/pybricks/pybricks-micropython/blob/master/CHANGELOG.md#300---2021-06-08
 [v3.1.0a1]: https://github.com/pybricks/pybricks-micropython/blob/master/CHANGELOG.md#310a1---2021-06-23
 [v3.1.0a2]: https://github.com/pybricks/pybricks-micropython/blob/master/CHANGELOG.md#310a2---2021-07-06
diff --git a/package.json b/package.json
index f1c9e4b0..7e09c02e 100644
--- a/package.json
+++ b/package.json
@@ -20,7 +20,7 @@
         "@testing-library/user-event": "^13.2.0",
         "@types/file-saver": "^2.0.3",
         "@types/jest": "^26.0.24",
-        "@types/node": "^12.20.16",
+        "@types/node": "^12.20.19",
         "@types/react": "^16.14.11",
         "@types/react-dom": "^16.9.14",
         "@types/react-redux": "^7.1.18",
@@ -92,7 +92,7 @@
         "eslint-plugin-prettier": "^3.4.0",
         "eslint-plugin-react": "^7.23.2",
         "eslint-plugin-total-functions": "^4.9.0",
-        "jest-mock-extended": "^1.0.18",
+        "jest-mock-extended": "^2.0.1",
         "prettier": "^2.3.2"
     }
 }
diff --git a/src/firmware/sagas.ts b/src/firmware/sagas.ts
index 792eb1be..dda1f939 100644
--- a/src/firmware/sagas.ts
+++ b/src/firmware/sagas.ts
@@ -55,6 +55,7 @@ import {
 import { RootState } from '../reducers';
 import { defined, hex, maybe } from '../utils';
 import { fmod, sumComplement32 } from '../utils/math';
+import { isAndroid } from '../utils/os';
 import {
     FailToFinishReasonType,
     FlashFirmwareActionType,
@@ -376,8 +377,9 @@ function* flashFirmware(action: FlashFirmwareFlashAction): Generator {
             yield* disconnectAndCancel();
         }
 
-        // 14 is "safe" size for all hubs
-        const maxDataSize = MaxProgramFlashSize.get(info.hubType) || 14;
+        // 14 is "safe" size for all hubs and Android
+        const maxDataSize =
+            (!isAndroid() && MaxProgramFlashSize.get(info.hubType)) || 14;
 
         let runningChecksum = 0xff;
 
diff --git a/src/utils/os.test.ts b/src/utils/os.test.ts
index 90c3d947..c21b28da 100644
--- a/src/utils/os.test.ts
+++ b/src/utils/os.test.ts
@@ -1,12 +1,23 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2021 The Pybricks Authors
 
-import { isMacOS, isWindows, prefersDarkMode } from './os';
+import { isAndroid, isMacOS, isWindows, prefersDarkMode } from './os';
 
 afterEach(() => {
     jest.resetAllMocks();
 });
 
+describe('isAndroid', () => {
+    test('is true', () => {
+        jest.spyOn(navigator, 'userAgent', 'get').mockReturnValue('Android');
+        expect(isAndroid()).toBeTruthy();
+    });
+    test('is false', () => {
+        jest.spyOn(navigator, 'userAgent', 'get').mockReturnValue('Linux');
+        expect(isAndroid()).toBeFalsy();
+    });
+});
+
 describe('isMacOS', () => {
     test('is true', () => {
         jest.spyOn(navigator, 'platform', 'get').mockReturnValue('MacIntel');
diff --git a/src/utils/os.ts b/src/utils/os.ts
index 12685d2e..5fe83dfd 100644
--- a/src/utils/os.ts
+++ b/src/utils/os.ts
@@ -3,6 +3,17 @@
 
 // Utility functions for dealing with operating systems.
 
+// TODO: replace with navigator.userAgentData when it is more widely available
+// https://developer.mozilla.org/en-US/docs/Web/API/User-Agent_Client_Hints_API
+
+/**
+ * Tests if we are running on Android.
+ * @returns `true` if running on Android, otherwise `false`.
+ */
+export function isAndroid(): boolean {
+    return /android/i.test(navigator.userAgent);
+}
+
 /**
  * Tests if we are running on macOS.
  * @returns `true` if running on macOS, otherwise `false`.
diff --git a/yarn.lock b/yarn.lock
index 72ff5bb9..2888fd33 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2044,10 +2044,10 @@
   resolved "https://registry.yarnpkg.com/@types/node/-/node-16.3.3.tgz#0c30adff37bbbc7a50eb9b58fae2a504d0d88038"
   integrity sha512-8h7k1YgQKxKXWckzFCMfsIwn0Y61UK6tlD6y2lOb3hTOIMlK3t9/QwHOhc81TwU+RMf0As5fj7NPjroERCnejQ==
 
-"@types/node@^12.20.16":
-  version "12.20.16"
-  resolved "https://registry.yarnpkg.com/@types/node/-/node-12.20.16.tgz#1acf34f6456208f495dac0434dd540488d17f991"
-  integrity sha512-6CLxw83vQf6DKqXxMPwl8qpF8I7THFZuIwLt4TnNsumxkp1VsRZWT8txQxncT/Rl2UojTsFzWgDG4FRMwafrlA==
+"@types/node@^12.20.19":
+  version "12.20.19"
+  resolved "https://registry.yarnpkg.com/@types/node/-/node-12.20.19.tgz#538e61fc220f77ae4a4663c3d8c3cb391365c209"
+  integrity sha512-niAuZrwrjKck4+XhoCw6AAVQBENHftpXw9F4ryk66fTgYaKQ53R4FI7c9vUGGw5vQis1HKBHDR1gcYI/Bq1xvw==
 
 "@types/normalize-package-data@^2.4.0":
   version "2.4.1"
@@ -7208,12 +7208,12 @@ jest-message-util@^26.6.0, jest-message-util@^26.6.2:
     slash "^3.0.0"
     stack-utils "^2.0.2"
 
-jest-mock-extended@^1.0.18:
-  version "1.0.18"
-  resolved "https://registry.yarnpkg.com/jest-mock-extended/-/jest-mock-extended-1.0.18.tgz#27a40e882c09f8230243fc6765fe7285b03f2b4b"
-  integrity sha512-qf1n7lIa2dTxxPIBr+FlXrbj3hnV1sG9DPZsrr2H/8W+Jw0wt6OmeOQsPcjRuW8EXIECC9pDXsSIfEdn+HP7JQ==
+jest-mock-extended@^2.0.1:
+  version "2.0.1"
+  resolved "https://registry.yarnpkg.com/jest-mock-extended/-/jest-mock-extended-2.0.1.tgz#5cc5085c2a3a83e301fd0eeba9ac82af4b3dc389"
+  integrity sha512-fOfes4i6a5991ZFzj9Un8nlFsSm2lpnJ9jRm6eT3kdtW8Bq9jdQiPYiCE2MHDiU5ySIbjzN4UkhCLAJ1jVtkaQ==
   dependencies:
-    ts-essentials "^7.0.2"
+    ts-essentials "^7.0.3"
 
 jest-mock@^26.6.2:
   version "26.6.2"
@@ -11878,10 +11878,10 @@ tryer@^1.0.1:
   resolved "https://registry.yarnpkg.com/tryer/-/tryer-1.0.1.tgz#f2c85406800b9b0f74c9f7465b81eaad241252f8"
   integrity sha512-c3zayb8/kWWpycWYg87P71E1S1ZL6b6IJxfb5fvsUgsf0S2MVGaDhDXXjDMpdCpfWXqptc+4mXwmiy1ypXqRAA==
 
-ts-essentials@^7.0.2:
-  version "7.0.2"
-  resolved "https://registry.yarnpkg.com/ts-essentials/-/ts-essentials-7.0.2.tgz#e21142df8034dbd444cb9573ed204d0b85fc64fb"
-  integrity sha512-qWPVC1xZGdefbsgFP7tPo+bsgSA2ZIXL1XeEe5M2WoMZxIOr/HbsHxP/Iv75IFhiMHMDGL7cOOwi5SXcgx9mHw==
+ts-essentials@^7.0.3:
+  version "7.0.3"
+  resolved "https://registry.yarnpkg.com/ts-essentials/-/ts-essentials-7.0.3.tgz#686fd155a02133eedcc5362dc8b5056cde3e5a38"
+  integrity sha512-8+gr5+lqO3G84KdiTSMRLtuyJ+nTBVRKuCrK4lidMPdVeEp0uqC875uE5NMcaA7YYMN7XsNiFQuMvasF8HT/xQ==
 
 ts-pnp@1.2.0, ts-pnp@^1.1.6:
   version "1.2.0"