diff --git a/.github/workflows/release-cut.yml b/.github/workflows/release-cut.yml
index 2c48d466305..0142518c4cb 100644
--- a/.github/workflows/release-cut.yml
+++ b/.github/workflows/release-cut.yml
@@ -1330,7 +1330,8 @@ jobs:
           }
 
           Copy-Item -Path $signedInstaller.FullName -Destination 'dist/orca-windows-setup.exe' -Force
-          & 'node_modules/app-builder-bin/win/x64/app-builder.exe' blockmap --input 'dist/orca-windows-setup.exe' --output 'dist/orca-windows-setup.exe.blockmap'
+          node config/scripts/generate-windows-blockmap.mjs 'dist/orca-windows-setup.exe' 'dist/orca-windows-setup.exe.blockmap'
+          if ($LASTEXITCODE -ne 0) { throw "blockmap generation failed with exit code $LASTEXITCODE" }
 
           $installer = Get-Item 'dist/orca-windows-setup.exe'
           $blockmap = Get-Item 'dist/orca-windows-setup.exe.blockmap'
diff --git a/.github/workflows/windows-signing-rehearsal.yml b/.github/workflows/windows-signing-rehearsal.yml
index 24b4307a83b..4ca080d803d 100644
--- a/.github/workflows/windows-signing-rehearsal.yml
+++ b/.github/workflows/windows-signing-rehearsal.yml
@@ -271,7 +271,7 @@ jobs:
             throw 'Signed Windows installer was not returned by SignPath.'
           }
           Copy-Item -Path $signedInstaller.FullName -Destination 'dist/orca-windows-setup.exe' -Force
-          & 'node_modules/app-builder-bin/win/x64/app-builder.exe' blockmap --input 'dist/orca-windows-setup.exe' --output 'dist/orca-windows-setup.exe.blockmap'
+          node config/scripts/generate-windows-blockmap.mjs 'dist/orca-windows-setup.exe' 'dist/orca-windows-setup.exe.blockmap'
           if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }
 
           $installer = Get-Item 'dist/orca-windows-setup.exe'
diff --git a/config/scripts/generate-windows-blockmap.mjs b/config/scripts/generate-windows-blockmap.mjs
new file mode 100644
index 00000000000..7444a7b43dc
--- /dev/null
+++ b/config/scripts/generate-windows-blockmap.mjs
@@ -0,0 +1,18 @@
+// Regenerate the electron-updater `.blockmap` for a (re-signed) Windows installer.
+// electron-builder 26 dropped the app-builder-bin Go binary; blockmap generation
+// now lives in app-builder-lib's pure-JS `buildBlockMap`. Mirrors createBlockmap's
+// "gzip" format for the standalone NSIS installer blockmap.
+import { createRequire } from 'node:module'
+
+const require = createRequire(import.meta.url)
+
+const [input, output] = process.argv.slice(2)
+if (!input || !output) {
+  console.error('usage: generate-windows-blockmap.mjs <input.exe> <output.exe.blockmap>')
+  process.exit(1)
+}
+
+const { buildBlockMap } = require('app-builder-lib/out/targets/blockmap/blockmap')
+
+const info = await buildBlockMap(input, 'gzip', output)
+console.log(`blockmap written: ${output} (installer sha512=${info.sha512}, size=${info.size})`)