diff --git a/.gitattributes b/.gitattributes
index 84c7add05..14c3c3594 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,4 +1,3 @@
 /Tests export-ignore
 /phpunit.xml.dist export-ignore
-/.gitattributes export-ignore
-/.gitignore export-ignore
+/.git* export-ignore
diff --git a/.github/PULL_REQUEST_TEMPLATE.md b/.github/PULL_REQUEST_TEMPLATE.md
new file mode 100644
index 000000000..4689c4dad
--- /dev/null
+++ b/.github/PULL_REQUEST_TEMPLATE.md
@@ -0,0 +1,8 @@
+Please do not submit any Pull Requests here. They will be closed.
+---
+
+Please submit your PR here instead:
+https://github.com/symfony/symfony
+
+This repository is what we call a "subtree split": a read-only subset of that main repository.
+We're looking forward to your PR there!
diff --git a/.github/workflows/check-subtree-split.yml b/.github/workflows/check-subtree-split.yml
new file mode 100644
index 000000000..16be48bae
--- /dev/null
+++ b/.github/workflows/check-subtree-split.yml
@@ -0,0 +1,37 @@
+name: Check subtree split
+
+on:
+  pull_request_target:
+
+jobs:
+  close-pull-request:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Close pull request
+      uses: actions/github-script@v6
+      with:
+        script: |
+          if (context.repo.owner === "symfony") {
+            github.rest.issues.createComment({
+              owner: "symfony",
+              repo: context.repo.repo,
+              issue_number: context.issue.number,
+              body: `
+          Thanks for your Pull Request! We love contributions.
+
+          However, you should instead open your PR on the main repository:
+          https://github.com/symfony/symfony
+
+          This repository is what we call a "subtree split": a read-only subset of that main repository.
+          We're looking forward to your PR there!
+          `
+            });
+
+            github.rest.pulls.update({
+              owner: "symfony",
+              repo: context.repo.repo,
+              pull_number: context.issue.number,
+              state: "closed"
+            });
+          }
diff --git a/Filesystem.php b/Filesystem.php
index 48c66a8e4..59a8bebe4 100644
--- a/Filesystem.php
+++ b/Filesystem.php
@@ -686,7 +686,7 @@ public function dumpFile(string $filename, $content)
                 throw new IOException(sprintf('Failed to write file "%s": ', $filename).self::$lastError, 0, null, $filename);
             }
 
-            self::box('chmod', $tmpFile, file_exists($filename) ? fileperms($filename) : 0666 & ~umask());
+            self::box('chmod', $tmpFile, @fileperms($filename) ?: 0666 & ~umask());
 
             $this->rename($tmpFile, $filename, true);
         } finally {
diff --git a/Tests/FilesystemTest.php b/Tests/FilesystemTest.php
index 2c222fd06..bc8a5ceca 100644
--- a/Tests/FilesystemTest.php
+++ b/Tests/FilesystemTest.php
@@ -14,6 +14,8 @@
 use Symfony\Component\Filesystem\Exception\InvalidArgumentException;
 use Symfony\Component\Filesystem\Exception\IOException;
 use Symfony\Component\Filesystem\Path;
+use Symfony\Component\Process\PhpExecutableFinder;
+use Symfony\Component\Process\Process;
 
 /**
  * Test class for Filesystem.
@@ -162,23 +164,32 @@ public function testCopyCreatesTargetDirectoryIfItDoesNotExist()
         $this->assertStringEqualsFile($targetFilePath, 'SOURCE FILE');
     }
 
-    /**
-     * @group network
-     */
     public function testCopyForOriginUrlsAndExistingLocalFileDefaultsToCopy()
     {
-        if (!\in_array('https', stream_get_wrappers())) {
-            $this->markTestSkipped('"https" stream wrapper is not enabled.');
+        if (!\in_array('http', stream_get_wrappers())) {
+            $this->markTestSkipped('"http" stream wrapper is not enabled.');
         }
-        $sourceFilePath = 'https://symfony.com/images/common/logo/logo_symfony_header.png';
-        $targetFilePath = $this->workspace.\DIRECTORY_SEPARATOR.'copy_target_file';
 
-        file_put_contents($targetFilePath, 'TARGET FILE');
+        $finder = new PhpExecutableFinder();
+        $process = new Process(array_merge([$finder->find(false)], $finder->findArguments(), ['-dopcache.enable=0', '-dvariables_order=EGPCS', '-S', 'localhost:8057']));
+        $process->setWorkingDirectory(__DIR__.'/Fixtures/web');
 
-        $this->filesystem->copy($sourceFilePath, $targetFilePath, false);
+        $process->start();
 
-        $this->assertFileExists($targetFilePath);
-        $this->assertEquals(file_get_contents($sourceFilePath), file_get_contents($targetFilePath));
+        do {
+            usleep(50000);
+        } while (!@fopen('http://localhost:8057', 'r'));
+
+        try {
+            $sourceFilePath = 'http://localhost:8057/logo_symfony_header.png';
+            $targetFilePath = $this->workspace.\DIRECTORY_SEPARATOR.'copy_target_file';
+            file_put_contents($targetFilePath, 'TARGET FILE');
+            $this->filesystem->copy($sourceFilePath, $targetFilePath, false);
+            $this->assertFileExists($targetFilePath);
+            $this->assertEquals(file_get_contents($sourceFilePath), file_get_contents($targetFilePath));
+        } finally {
+            $process->stop();
+        }
     }
 
     public function testMkdirCreatesDirectoriesRecursively()
diff --git a/Tests/Fixtures/web/index.php b/Tests/Fixtures/web/index.php
new file mode 100644
index 000000000..b3d9bbc7f
--- /dev/null
+++ b/Tests/Fixtures/web/index.php
@@ -0,0 +1 @@
+<?php
diff --git a/Tests/Fixtures/web/logo_symfony_header.png b/Tests/Fixtures/web/logo_symfony_header.png
new file mode 100644
index 000000000..519ab7c69
Binary files /dev/null and b/Tests/Fixtures/web/logo_symfony_header.png differ
diff --git a/composer.json b/composer.json
index 10a7a531c..be9da2f61 100644
--- a/composer.json
+++ b/composer.json
@@ -18,7 +18,8 @@
     "require": {
         "php": ">=8.1",
         "symfony/polyfill-ctype": "~1.8",
-        "symfony/polyfill-mbstring": "~1.8"
+        "symfony/polyfill-mbstring": "~1.8",
+        "symfony/process": "^5.4|^6.4"
     },
     "autoload": {
         "psr-4": { "Symfony\\Component\\Filesystem\\": "" },