diff --git a/.github/workflows/build-php.yml b/.github/workflows/build-php.yml
index b5f6cf8..d86a30e 100644
--- a/.github/workflows/build-php.yml
+++ b/.github/workflows/build-php.yml
@@ -220,8 +220,14 @@ jobs:
   build-windows-amd64:
     name: Windows x64
     needs: resolve-version
-    runs-on: windows-latest
+    # Not windows-latest or windows-2025: those images now ship Visual Studio
+    # 2026, and static-php-cli only looks for 2022 or 2019, so its doctor check
+    # fails before anything is built.
+    runs-on: windows-2022
     steps:
+      - name: Check out repository code
+        uses: actions/checkout@v7
+
       - name: Clone static-php-cli
         run: |
           git clone --depth 1 --branch ${{ env.SPC_VERSION }} https://github.com/crazywhalecc/static-php-cli.git spc
@@ -238,6 +244,12 @@ jobs:
           cd spc
           composer install --no-dev --classmap-authoritative
 
+      # Schannel cannot use a CA file and the Windows certificate store
+      # together, which the CLI needs. This must run before the download step,
+      # which reads the dependencies it changes.
+      - name: Build curl against OpenSSL, not Schannel
+        run: php scripts/patch-spc-windows-curl.php spc
+
       - name: Setup build environment
         run: |
           cd spc
@@ -259,6 +271,18 @@ jobs:
           $extensions = $extensions.Trim(',')
           ./bin/spc build "$extensions" --build-cli ${{ inputs.debug && '--debug' || '' }}
 
+      # The CLI depends on the SSL backend: only OpenSSL can use a CA file and
+      # the Windows certificate store together.
+      - name: Check the SSL backend
+        run: |
+          $curl = & ./spc/buildroot/bin/php.exe -n -r "echo curl_version()['ssl_version'];"
+          $openssl = & ./spc/buildroot/bin/php.exe -n -r "echo OPENSSL_VERSION_TEXT;"
+          Write-Host "curl: $curl"
+          Write-Host "openssl extension: $openssl"
+          if ($curl -notlike 'OpenSSL/*') {
+            throw "expected curl to be built against OpenSSL, got '$curl'"
+          }
+
       - name: Upload artifact
         uses: actions/upload-artifact@v7
         with:
diff --git a/README.md b/README.md
index dc9ab35..f1dd270 100644
--- a/README.md
+++ b/README.md
@@ -67,6 +67,22 @@ The workflow will:
 - **Linux/macOS**: static-php-cli automatically uses the system CA bundle
 - **Windows**: Requires explicit `cacert.pem` configuration (handled by the CLI)
 
+### Windows SSL backend
+
+static-php-cli builds curl with Schannel on Windows. These builds change that to
+OpenSSL, which is already built for the `openssl` extension, using
+`scripts/patch-spc-windows-curl.php`.
+
+Schannel verifies against a CA file *instead of* the Windows certificate store,
+and refuses a file larger than 1 MiB. The CLI has to pass a CA file, because the
+`openssl` extension cannot read the store at all, so with Schannel a root
+certificate installed by an organization is never trusted. curl built against
+OpenSSL loads a CA file and the Windows stores together, and has no size limit.
+
+The patch fails the build if static-php-cli changes in a way it does not expect,
+rather than quietly producing a Schannel build. See
+[upsun/cli#110](https://github.com/upsun/cli/issues/110).
+
 ## License
 
 The build scripts in this repository are MIT licensed. PHP binaries are subject to the [PHP License](https://www.php.net/license/).
diff --git a/scripts/patch-spc-windows-curl.php b/scripts/patch-spc-windows-curl.php
new file mode 100644
index 0000000..b2d8b65
--- /dev/null
+++ b/scripts/patch-spc-windows-curl.php
@@ -0,0 +1,107 @@
+<?php
+
+/**
+ * Builds curl against OpenSSL instead of Schannel, on Windows.
+ *
+ * static-php-cli builds curl with Schannel. Schannel cannot combine a CA file
+ * with the Windows certificate store: given a file it verifies against that
+ * file alone, so an organization's own root certificate, which is installed in
+ * the store, is not seen. It also refuses a CA file larger than 1 MiB, which a
+ * bundle including the store's certificates can exceed. The CLI needs a CA
+ * file, because the openssl extension cannot read the store at all, so with
+ * Schannel there is no way to trust both sets of certificates.
+ *
+ * curl built against OpenSSL loads a CA file and the Windows stores together,
+ * and has no size limit. OpenSSL is already built here for the openssl
+ * extension.
+ *
+ * See https://github.com/upsun/cli/issues/110, and
+ * https://github.com/crazywhalecc/static-php-cli/pull/674 which chose Schannel.
+ *
+ * Usage: php scripts/patch-spc-windows-curl.php [path to static-php-cli]
+ */
+
+declare(strict_types=1);
+
+$spcDir = $argv[1] ?? 'spc';
+
+/**
+ * Stops with a message, so that a build never quietly uses the wrong backend.
+ */
+function fail(string $message): never
+{
+    fwrite(STDERR, 'patch-spc-windows-curl: ' . $message . PHP_EOL);
+    exit(1);
+}
+
+function readFileOrFail(string $path): string
+{
+    if (!is_file($path)) {
+        fail("$path does not exist: check the static-php-cli version");
+    }
+    $contents = file_get_contents($path);
+    if ($contents === false) {
+        fail("could not read $path");
+    }
+    return $contents;
+}
+
+function writeFileOrFail(string $path, string $contents): void
+{
+    if (file_put_contents($path, $contents) === false) {
+        fail("could not write $path");
+    }
+}
+
+// curl needs the OpenSSL library on Windows. static-php-cli removed it from
+// curl's dependencies when it switched to Schannel, and without it the build
+// order does not guarantee OpenSSL is there first.
+$libFile = $spcDir . '/config/lib.json';
+$libs = json_decode(readFileOrFail($libFile), true);
+if (!is_array($libs) || !isset($libs['curl']['lib-depends-windows']) || !is_array($libs['curl']['lib-depends-windows'])) {
+    fail("$libFile does not list curl's Windows dependencies: check the static-php-cli version");
+}
+if (in_array('openssl', $libs['curl']['lib-depends-windows'], true)) {
+    echo "curl already depends on openssl on Windows\n";
+} else {
+    array_unshift($libs['curl']['lib-depends-windows'], 'openssl');
+    writeFileOrFail($libFile, json_encode($libs, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE) . "\n");
+    echo "added openssl to curl's Windows dependencies\n";
+}
+
+// Choose the backend in the cmake options curl is built with.
+$curlFile = $spcDir . '/src/SPC/builder/windows/library/curl.php';
+$source = readFileOrFail($curlFile);
+$options = [
+    "'-DUSE_WINDOWS_SSPI=ON '" => "'-DUSE_WINDOWS_SSPI=OFF '",
+    "'-DCURL_USE_SCHANNEL=ON '" => "'-DCURL_USE_SCHANNEL=OFF '",
+    "'-DCURL_USE_OPENSSL=OFF '" => "'-DCURL_USE_OPENSSL=ON '",
+];
+foreach ($options as $from => $to) {
+    if (substr_count($source, $to) === 1 && !str_contains($source, $from)) {
+        echo "already set: $to\n";
+        continue;
+    }
+    if (substr_count($source, $from) !== 1) {
+        fail("expected exactly one $from in $curlFile: check the static-php-cli version");
+    }
+    $source = str_replace($from, $to, $source);
+    echo "set $to\n";
+}
+
+// Use the Windows certificate store when no CA file is set, which is what
+// Schannel did. Only then: given a CA file, curl uses that alone unless asked
+// for both. This keeps verification working if the CLI cannot write its bundle.
+$nativeCA = "'-DCURL_CA_NATIVE=ON '";
+$anchor = "'-DCURL_ENABLE_SSL=ON ' .";
+if (str_contains($source, $nativeCA)) {
+    echo "already set: $nativeCA\n";
+} else {
+    if (substr_count($source, $anchor) !== 1) {
+        fail("expected exactly one $anchor in $curlFile: check the static-php-cli version");
+    }
+    $source = str_replace($anchor, $nativeCA . " .\n                " . $anchor, $source);
+    echo "set $nativeCA\n";
+}
+
+writeFileOrFail($curlFile, $source);