diff --git a/apps/desktop/electron/fixtures/windows-system-ca.ts b/apps/desktop/electron/fixtures/windows-system-ca.ts
new file mode 100644
index 0000000000..3f5d636c2f
--- /dev/null
+++ b/apps/desktop/electron/fixtures/windows-system-ca.ts
@@ -0,0 +1,37 @@
+// Synthetic self-signed CAs; no private keys are retained. Tests freeze time
+// between the expired root's 2025 expiry and the other roots' 2035 expiry.
+export const bundledRoot = `-----BEGIN CERTIFICATE-----
+MIIBWDCB/6ADAgECAhRU6TyqBZA4z6kjw80UZ4JJcTGTezAKBggqhkjOPQQDAjAi
+MSAwHgYDVQQDDBdIZXJtZXMgdGVzdCBidW5kbGVkUm9vdDAeFw0yMDAxMDEwMDAw
+MDBaFw0zNTAxMDEwMDAwMDBaMCIxIDAeBgNVBAMMF0hlcm1lcyB0ZXN0IGJ1bmRs
+ZWRSb290MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEzYsepxCA6/L5jOtyaK7c
+tonILmwaEH7S3SaXZkCPMPPn7ciN08fFIQvEK2xmexibsIW/07/y+EQsCsytdXD7
+TqMTMBEwDwYDVR0TAQH/BAUwAwEB/zAKBggqhkjOPQQDAgNIADBFAiAoOvvNIWtl
+56kb5jeS67rndvpGdvRVfA8hu/d7qPUXHgIhAOVWB0FmymX7/ptbzS9os2DB7S8M
+bsTP81ca6H4QAVMO
+-----END CERTIFICATE-----
+`
+
+export const privateRoot = `-----BEGIN CERTIFICATE-----
+MIIBWDCB/6ADAgECAhQpNQF0JRsR2+tIXdZrGV71uQLqnjAKBggqhkjOPQQDAjAi
+MSAwHgYDVQQDDBdIZXJtZXMgdGVzdCBwcml2YXRlUm9vdDAeFw0yMDAxMDEwMDAw
+MDBaFw0zNTAxMDEwMDAwMDBaMCIxIDAeBgNVBAMMF0hlcm1lcyB0ZXN0IHByaXZh
+dGVSb290MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEbWaJLnFzm5gFQFK4u1Sg
++ZSXFpfKOuKVLiLU9K2xfg9glPZQY+25Eh+7eMkeOWbOOgXbQE9gmQ2Lsjs+G57C
+fqMTMBEwDwYDVR0TAQH/BAUwAwEB/zAKBggqhkjOPQQDAgNIADBFAiAuMyPaHvKJ
+BTNIxn3kTlG/7rQ8iSBJ/iTYSxC/7sLzcwIhAJZno/XUb+l9XQfNgADj7jHRorx7
+Hfp7kgJ01+X1LAKU
+-----END CERTIFICATE-----
+`
+
+export const expiredRoot = `-----BEGIN CERTIFICATE-----
+MIIBWDCB/6ADAgECAhQpDur4nw/PAq6RuWUbTzDvuICiojAKBggqhkjOPQQDAjAi
+MSAwHgYDVQQDDBdIZXJtZXMgdGVzdCBleHBpcmVkUm9vdDAeFw0yMDAxMDEwMDAw
+MDBaFw0yNTAxMDEwMDAwMDBaMCIxIDAeBgNVBAMMF0hlcm1lcyB0ZXN0IGV4cGly
+ZWRSb290MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEe+50enZvxfDciM9yMPBo
+BHYtfdV4eSv017W1GgC3OyDQpypA7Usio1jSy6VXGSGTKpKVPTeMhTPtQLSpbf2z
+eKMTMBEwDwYDVR0TAQH/BAUwAwEB/zAKBggqhkjOPQQDAgNIADBFAiAduJa3QWjS
++lF7cmuGdgUezYQLEIUqAPsPhJxgzGNmiwIhAKIyQ1uxv4Mzl0Mou7AiUGpqy8Xr
+CKxqXEB0ODeqpB0N
+-----END CERTIFICATE-----
+`
diff --git a/apps/desktop/electron/windows-system-ca.test.ts b/apps/desktop/electron/windows-system-ca.test.ts
index d7e408bd24..164d931c8f 100644
--- a/apps/desktop/electron/windows-system-ca.test.ts
+++ b/apps/desktop/electron/windows-system-ca.test.ts
@@ -1,9 +1,36 @@
 import assert from 'node:assert/strict'
+import { X509Certificate } from 'node:crypto'
 
-import { test } from 'vitest'
+import { afterEach, test, vi } from 'vitest'
 
+import { bundledRoot, expiredRoot, privateRoot } from './fixtures/windows-system-ca'
 import { installWindowsSystemCaTrust, type NodeTlsCaApi } from './windows-system-ca'
 
+afterEach(() => vi.restoreAllMocks())
+
+test('excludes expired roots and deduplicates real certificates with defaults first', () => {
+  vi.spyOn(Date, 'now').mockReturnValue(new Date('2026-01-01T00:00:00Z').getTime())
+  const tlsApi = fakeTlsApi(
+    [expiredRoot, bundledRoot, bundledRoot, 'unparseable-default'],
+    [expiredRoot, bundledRoot.replaceAll('\n', '\r\n'), privateRoot, privateRoot, 'unparseable-system']
+  )
+
+  const result = installWindowsSystemCaTrust(tlsApi, 'win32')
+
+  assert.deepEqual(tlsApi.installed, [[bundledRoot, 'unparseable-default', privateRoot, 'unparseable-system']])
+  assert.deepEqual(result, { applied: true, systemCertificateCount: 2, totalCertificateCount: 4 })
+})
+
+test('excludes a root at its exact expiry while retaining valid defaults', () => {
+  vi.spyOn(Date, 'now').mockReturnValue(new X509Certificate(expiredRoot).validToDate.getTime())
+  const tlsApi = fakeTlsApi([bundledRoot], [expiredRoot])
+
+  const result = installWindowsSystemCaTrust(tlsApi, 'win32')
+
+  assert.deepEqual(tlsApi.installed, [[bundledRoot]])
+  assert.deepEqual(result, { applied: true, systemCertificateCount: 0, totalCertificateCount: 1 })
+})
+
 function fakeTlsApi(
   defaults: string[] = ['bundled-ca', 'extra-ca'],
   system: string[] = ['windows-root-ca']
@@ -34,7 +61,7 @@ test('installs Windows system CAs without dropping existing defaults', () => {
   })
 })
 
-test('does not inspect or replace CAs outside Windows', () => {
+test.each(['darwin', 'linux'] as const)('does not inspect or replace CAs on %s', platform => {
   let reads = 0
 
   const tlsApi: NodeTlsCaApi = {
@@ -48,7 +75,7 @@ test('does not inspect or replace CAs outside Windows', () => {
     }
   }
 
-  const result = installWindowsSystemCaTrust(tlsApi, 'darwin')
+  const result = installWindowsSystemCaTrust(tlsApi, platform)
 
   assert.equal(reads, 0)
   assert.deepEqual(result, {
diff --git a/apps/desktop/electron/windows-system-ca.ts b/apps/desktop/electron/windows-system-ca.ts
index f4406fdd42..a2cecce08b 100644
--- a/apps/desktop/electron/windows-system-ca.ts
+++ b/apps/desktop/electron/windows-system-ca.ts
@@ -1,3 +1,5 @@
+import { X509Certificate } from 'node:crypto'
+
 interface NodeTlsCaApi {
   getCACertificates(type?: 'default' | 'system'): string[]
   setDefaultCACertificates(certificates: string[]): void
@@ -31,12 +33,35 @@ function installWindowsSystemCaTrust(tlsApi: NodeTlsCaApi, platform = process.pl
       }
     }
 
-    const certificates = [...defaultCertificates, ...systemCertificates]
+    // Prefer existing defaults. Expired Windows roots can divert OpenSSL onto
+    // an expired chain even when a valid bundled trust path exists.
+    const seen = new Set<string>()
+    const now = Date.now()
+
+    const keepCertificate = (pem: string): boolean => {
+      try {
+        const certificate = new X509Certificate(pem)
+
+        if (certificate.validToDate.getTime() <= now || seen.has(certificate.fingerprint256)) {
+          return false
+        }
+        seen.add(certificate.fingerprint256)
+      } catch {
+        // Leave PEM acceptability to Node if its X.509 parser cannot inspect it.
+      }
+
+      return true
+    }
+
+    const filteredDefaults = defaultCertificates.filter(keepCertificate)
+    const filteredSystem = systemCertificates.filter(keepCertificate)
+    const certificates = [...filteredDefaults, ...filteredSystem]
+
     tlsApi.setDefaultCACertificates(certificates)
 
     return {
       applied: true,
-      systemCertificateCount: systemCertificates.length,
+      systemCertificateCount: filteredSystem.length,
       totalCertificateCount: certificates.length
     }
   } catch (error) {
diff --git a/contributors/emails/215755014+Stoltemberg@users.noreply.github.com b/contributors/emails/215755014+Stoltemberg@users.noreply.github.com
new file mode 100644
index 0000000000..38b203b47c
--- /dev/null
+++ b/contributors/emails/215755014+Stoltemberg@users.noreply.github.com
@@ -0,0 +1 @@
+Stoltemberg
diff --git a/contributors/emails/249166551+wliu-dev@users.noreply.github.com b/contributors/emails/249166551+wliu-dev@users.noreply.github.com
new file mode 100644
index 0000000000..250b3c2fb7
--- /dev/null
+++ b/contributors/emails/249166551+wliu-dev@users.noreply.github.com
@@ -0,0 +1 @@
+wliu-dev