diff --git a/.github/workflows/Test.yml b/.github/workflows/Test.yml
index eb3585b..4c391c5 100644
--- a/.github/workflows/Test.yml
+++ b/.github/workflows/Test.yml
@@ -699,3 +699,47 @@ jobs:
       run: |
         uname -a
         openssl help
+
+
+  main-mirror:
+    name: 🔒 main-mirror-only
+    needs: [cache]
+    runs-on: windows-latest
+    steps:
+    - name: 🧰 Checkout
+      uses: actions/checkout@v6
+      with:
+        persist-credentials: false
+    - name: 📥 Download artifact
+      uses: actions/download-artifact@v7
+      with:
+        name: action
+    - name: 🚧 run action
+      uses: ./
+      with:
+        update: true
+        install: git
+      env:
+        __SETUP_MSYS2_USE_MAIN_MIRROR_ONLY: 'true'
+    - shell: msys2 {0}
+      run: |
+        # Verify pacman-conf.exe output doesn't contain mirror.msys2.org
+        echo "Checking pacman-conf.exe output:"
+        pacman-conf.exe
+        if pacman-conf.exe | grep -q 'mirror\.msys2\.org'; then
+          echo "ERROR: pacman-conf.exe output contains mirror.msys2.org"
+          exit 1
+        fi
+        echo "✓ No mirror.msys2.org found in pacman-conf.exe output"
+
+        # Verify mirrorlist files only contain repo.msys2.org
+        echo "Checking mirrorlist.mingw:"
+        cat /etc/pacman.d/mirrorlist.mingw
+        grep -q 'repo.msys2.org/mingw' /etc/pacman.d/mirrorlist.mingw
+        [ $(wc -l < /etc/pacman.d/mirrorlist.mingw) -eq 1 ] || exit 1
+        echo "Checking mirrorlist.msys:"
+        cat /etc/pacman.d/mirrorlist.msys
+        grep -q 'repo.msys2.org/msys' /etc/pacman.d/mirrorlist.msys
+        [ $(wc -l < /etc/pacman.d/mirrorlist.msys) -eq 1 ] || exit 1
+
+        git --version
diff --git a/main.js b/main.js
index 64ff3f7..6e76dc7 100644
--- a/main.js
+++ b/main.js
@@ -44,6 +44,8 @@ class Input {
         this.location;
         /** @type {boolean} */
         this.cache;
+        /** @type {boolean} */
+        this.usemainmirroronly;
     }
 }
 
@@ -61,6 +63,14 @@ function parseInput() {
   let p_location = core.getInput('location');
   let p_cache = core.getBooleanInput('cache');
 
+  // Configures pacman to use only repo.msys2.org instead of the mirrorlist.
+  // See: https://github.com/msys2/setup-msys2/issues/571
+  let p_use_main_mirror_only = false;
+  const envValue = process.env['__SETUP_MSYS2_USE_MAIN_MIRROR_ONLY'];
+  if (envValue === 'true' || envValue === '1') {
+    p_use_main_mirror_only = true;
+  }
+
   const msystem_allowed = ['MSYS', 'MINGW32', 'MINGW64', 'UCRT64', 'CLANG64', 'CLANGARM64'];
   if (!msystem_allowed.includes(p_msystem.toUpperCase())) {
     throw new Error(`'msystem' needs to be one of ${ msystem_allowed.join(', ') }, got ${p_msystem}`);
@@ -85,6 +95,7 @@ function parseInput() {
   input.platformcheckseverity = p_platformcheckseverity;
   input.location = (p_location == "RUNNER_TEMP") ? process.env['RUNNER_TEMP'] : p_location;
   input.cache = p_cache;
+  input.usemainmirroronly = p_use_main_mirror_only;
 
   return input;
 }
@@ -136,6 +147,18 @@ async function disableKeyRefresh(msysRootDir) {
   await fs.promises.writeFile(postFile, newContent, 'utf8');
 }
 
+/**
+ * @param {string} msysRootDir
+ * @returns {Promise<void>}
+ */
+async function configureMainMirror(msysRootDir) {
+  const mirrorlistMingw = path.join(msysRootDir, 'etc', 'pacman.d', 'mirrorlist.mingw');
+  const mirrorlistMsys = path.join(msysRootDir, 'etc', 'pacman.d', 'mirrorlist.msys');
+
+  await fs.promises.writeFile(mirrorlistMingw, 'Server = https://repo.msys2.org/mingw/$repo/\n', 'utf8');
+  await fs.promises.writeFile(mirrorlistMsys, 'Server = https://repo.msys2.org/msys/$arch/\n', 'utf8');
+}
+
 /**
  * @param {string[]} paths
  * @param {string} restoreKey
@@ -200,7 +223,7 @@ class PackageCache {
     // We want a cache key that is ideally always the same for the same kind of job.
     // So that mingw32 and ming64 jobs, and jobs with different install packages have different caches.
     let shasum = crypto.createHash('sha1');
-    shasum.update([CACHE_FLUSH_COUNTER, input.release, input.update, input.pathtype, input.msystem, input.install].toString() + INSTALLER_CHECKSUM);
+    shasum.update([CACHE_FLUSH_COUNTER, input.release, input.update, input.pathtype, input.msystem, input.install, input.usemainmirroronly].toString() + INSTALLER_CHECKSUM);
     this.jobCacheKey = this.fallbackCacheKey + '-conf:' + shasum.digest('hex').slice(0, 8);
 
     this.restoreKey = undefined;
@@ -390,6 +413,12 @@ async function run() {
       core.endGroup();
     }
 
+    if (input.usemainmirroronly) {
+      core.startGroup('Configuring main mirror...');
+      await configureMainMirror(msysRootDir);
+      core.endGroup();
+    }
+
     core.startGroup('Disable CheckSpace...');
     // Reduce time required to install packages by disabling pacman's disk space checking
     await runMsys(['sed', '-i', 's/^CheckSpace/#CheckSpace/g', '/etc/pacman.conf']);