Signal Desktop fails to start due to "Cannot use import statement outside a module" on Windows 11 25H2

[rhdehf1030]

Using a supported version?

• I have searched searched open and closed issues for duplicates.
• I am using Signal-Desktop as provided by the Signal team, not a 3rd-party package.

Overall summary

Signal Desktop fails to launch properly due to a preload script error.
The application throws a SyntaxError related to the usage of the import statement outside a module context, specifically in @signalapp/libsignal-client.

Steps to reproduce

1. Install Signal Desktop using the official installer on Windows.
2. Launch the application.
3. Observe that Signal does not load properly and shows errors in the developer console.

Expected result

Signal Desktop should start without any JavaScript errors and load the user interface as expected.

Actual result

The following error appears in the developer console and prevents the app from launching:

preload error! <redacted-path>/resources/app.asar/node_modules/@signalapp/libsignal-client/dist/index.js:5
import { Buffer } from 'node:buffer';
^^^^^^

SyntaxError: Failed to construct 'ContextifyScript': Cannot use import statement outside a module
    at makeContextifyScript (node:internal/vm:185:14)
    at wrapSafe (node:internal/modules/cjs/loader:1609:20)
    at Module._compile (node:internal/modules/cjs/loader:1687:20)
    ...
background.html:136 Uncaught TypeError: window.startApp is not a function

and main.log shows

{"level":30,"time":"2025-10-19T07:12:51.859Z","msg":"[startup_config] Set Windows Application User Model ID (AUMID) {\"AUMID\":\"org.whispersystems.signal-desktop\"}"}
{"level":30,"time":"2025-10-19T07:12:51.891Z","msg":"[base_config] config/get: Successfully read user config file"}
{"level":30,"time":"2025-10-19T07:12:52.021Z","msg":"[base_config] config/get: Successfully read ephemeral config file"}
{"level":30,"time":"2025-10-19T07:12:52.146Z","msg":"[app/main] making app single instance"}
{"level":30,"time":"2025-10-19T07:12:52.519Z","msg":"[app/main] got fast localeOverride setting null"}
{"level":30,"time":"2025-10-19T07:12:52.520Z","msg":"[app/main] app.ready: hour cycle preference: UnknownPreference"}
...
{"level":30,"time":"2025-10-19T07:12:52.710Z","msg":"[spell_check] spellcheck: setting languages to: [\"ko\"]"}
{"level":40,"time":"2025-10-19T07:12:53.193Z","msg":"[app/main] MainSQL: sqlite(SQLITE_NOTICE_RECOVER_WAL): recovered 5 frames from WAL file [REDACTED]\\sql\\db.sqlite-wal"}
{"level":30,"time":"2025-10-19T07:12:53.201Z","msg":"[app/main] MainSQL: updateSchema:\n  Current user_version: 1480;\n  Most recent db schema: 1480;\n  SQLite version: 3.50.4;\n  SQLCipher version: 4.10.0 community;\n  (deprecated) schema_version: 567;\n"}
{"level":30,"time":"2025-10-19T07:12:54.329Z","msg":"[app/main] got fast theme-setting value light"}
{"level":50,"time":"2025-10-19T07:12:54.469Z","msg":"[app/main] Preload error in [REDACTED]\\preload.wrapper.js:  Failed to construct 'ContextifyScript': Cannot use import statement outside a module"}
{"level":30,"time":"2025-10-19T07:12:54.583Z","msg":"[app/main] main window is ready-to-show"}
{"level":30,"time":"2025-10-19T07:12:54.603Z","msg":"[SystemTrayService] System tray service: created"}
{"level":30,"time":"2025-10-19T07:12:54.603Z","msg":"[SystemTrayService] System tray service: updating main window. Previously, there was not a window, and now there is"}
{"level":30,"time":"2025-10-19T07:12:54.603Z","msg":"[SystemTrayService] System tray service: rendering no tray"}
{"level":30,"time":"2025-10-19T07:12:54.603Z","msg":"[SystemTrayService] System tray service: enabling"}
{"level":30,"time":"2025-10-19T07:12:54.604Z","msg":"[SystemTrayService] System tray service: rendering the tray"}
{"level":30,"time":"2025-10-19T07:12:54.604Z","msg":"[SystemTrayService] System tray service: creating the tray"}

Screenshots

No response

Signal version

7.75.1 Production

Operating system

Windows 11 25H2

Version of Signal on your phone

No response

Link to debug log

No response

[whitecloudy]

I have same issue here. Reinstalled several time while checking that all the files inside "AppData\Roaming\Signal" are gone. But that did not fix the problem. My log is almost same which includes

Preload error in [REDACTED]\\preload.wrapper.js:  Failed to construct 'ContextifyScript': Cannot use import statement outside a module"

[Teaster]

I have same issue here

[scottnonnenberg-signal]

@rhdehf1030 @whitecloudy @Teaster Our theory is that, for some reason, Signal Desktop only partially installed, and you have a combination of old and new files.

@whitecloudy I see that you installed multiple times, but AppData\Roaming\Signal is where your data is stored, not where the application is installed. You'll want to look at AppData\Local\Programs\signal-desktop\.

What I'd recommend for all of you is rebooting (to unlock files), then installing afresh from https://signal.org

Let me know - did that make things work?

[whitecloudy]

@scottnonnenberg-signal Thanks for your kind respond, but I'm afraid that did not work either.

I reboot my PC while deactivate "running the Signal on boot" for clean uninstall. I uninstalled and explicitly checked no files exist in AppData\Roaming\Signal or AppData\Local\Programs\signal-desktop.(I checked 'AppData\Roaming\Signal` because there might some temporary file could exists and it could cause problem.)

I reboot again just to make sure and installed the Signal. But same thing happend again. Same symptom and same log.

[whitecloudy]

@scottnonnenberg-signal I somehow managed to find 7.74.0 and 7.75.0 installer. The 7.74.0 works perfectly fine. I reinstalled 7.75.1 and 7.75.0, both of them have the symptom. Back to 7.74.0, it works fine.

In conclusion, there may be a problem with 7.75.0.

[rhdehf1030]

It looks like converting libsignal to ESM might have broken something. Could someone please test it?

signalapp/libsignal@1f01c19

[scottnonnenberg-signal]

I'm running 7.75.1 just fine on my Windows 2011 25H2 install, which is on an ARM machine. Are you all on Intel processors or ARM processors?

@whitecloudy Are you sure you're still getting the same error? We're seeing other errors on Window 25H2, where people need to update their drivers: #7543

[scottnonnenberg-signal]

Please also consider trying the beta, to see if you see the same problems there: https://support.signal.org/hc/en-us/articles/360007318471-Signal-Beta

[rhdehf1030]

@scottnonnenberg-signal

Please also consider trying the beta, to see if you see the same problems there: https://support.signal.org/hc/en-us/articles/360007318471-Signal-Beta

I've already tried installing it, but unfortunately it didn't work
And I’m using an x86 CPU, not an ARM CPU, as I’m on a Surface Pro 7
The same issue occurred on other PCs with 24H2 as well

[whitecloudy]

@scottnonnenberg-signal
Still same error, the Signal does not show anything such as message or even registration QR code but the weird blue message imoji that we usally see in the inital program launch. And same error log appears.#7547 (comment)

I am using AMD CPU but I don't think that is related, nor the 25H2 too.

[scottnonnenberg-signal]

@whitecloudy When you say "Still same error" what scenario do you mean? Did you install the beta?

@rhdehf1030 If you open the signal install directory AppData\Local\Programs\signal-desktop and look at the file versions and dates available there, what do you see? A full listing would be helpful for us. If you don't want to provide that here, please consider reaching out to Signal Support: https://support.signal.org/hc/en-us/requests/new

[rhdehf1030]

@scottnonnenberg-signal
I've finally identified the root cause and found a temporary solution to the issue.
The problem was caused by the default Korean encoding in Windows, which corrupted the asar file path.

Temporary solution is here:
https://learn.microsoft.com/en-us/windows/apps/design/globalizing/use-utf8-code-page

Unfortunately, I didn't have time to check if there is a related commit.
Please check and fix it.

@whitecloudy
You're a Korean developer too, right? So I'm guessing you must have faced the same issue as me ㅋㅋㅋㅋ

[scottnonnenberg-signal]

Oh, wow! What was the corrupt path?