diff --git a/.github/workflows/continuous-integration.yml b/.github/workflows/continuous-integration.yml
index d98b34fc1..1e3f99b46 100644
--- a/.github/workflows/continuous-integration.yml
+++ b/.github/workflows/continuous-integration.yml
@@ -103,6 +103,21 @@ jobs:
       - name: "Run install again using composer binary from source"
         run: "bin/composer install ${{ env.COMPOSER_FLAGS }}"
 
+      - name: "Make source binary the one used by default (Linux / macOS)"
+        if: "!contains(matrix.os, 'windows')"
+        run: |
+          echo -e "$(pwd)/bin\n$(cat $GITHUB_PATH)" > $GITHUB_PATH
+          echo -e "COMPOSER_BINARY=$(pwd)/bin/composer" >> $GITHUB_ENV
+
+      - name: "Make source binary the one used by default (Windows)"
+        if: "contains(matrix.os, 'windows')"
+        run: |
+          $(
+              (echo "$(Get-Location)\bin")
+              (Get-Content $env:GITHUB_PATH -Raw)
+          ) | Set-Content $env:GITHUB_PATH
+          echo "COMPOSER_BINARY=$(Get-Location)\bin\composer" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
+
       - name: "Prepare git environment"
         run: "git config --global user.name composer && git config --global user.email composer@example.com"
 
diff --git a/src/Composer/Autoload/ClassLoader.php b/src/Composer/Autoload/ClassLoader.php
index 3a8ed4886..fd56bd7d8 100644
--- a/src/Composer/Autoload/ClassLoader.php
+++ b/src/Composer/Autoload/ClassLoader.php
@@ -43,7 +43,7 @@ namespace Composer\Autoload;
 class ClassLoader
 {
     /** @var \Closure(string):void */
-    private $includeFile;
+    private static $includeFile;
 
     /** @var ?string */
     private $vendorDir;
@@ -109,18 +109,7 @@ class ClassLoader
     public function __construct($vendorDir = null)
     {
         $this->vendorDir = $vendorDir;
-
-        /**
-         * Scope isolated include.
-         *
-         * Prevents access to $this/self from included files.
-         *
-         * @param  string $file
-         * @return void
-         */
-        $this->includeFile = static function($file) {
-            include $file;
-        };
+        self::initializeIncludeClosure();
     }
 
     /**
@@ -440,7 +429,7 @@ class ClassLoader
     public function loadClass($class)
     {
         if ($file = $this->findFile($class)) {
-            ($this->includeFile)($file);
+            (self::$includeFile)($file);
 
             return true;
         }
@@ -570,4 +559,23 @@ class ClassLoader
 
         return false;
     }
+
+    private static function initializeIncludeClosure(): void
+    {
+        if (self::$includeFile !== null) {
+            return;
+        }
+
+        /**
+         * Scope isolated include.
+         *
+         * Prevents access to $this/self from included files.
+         *
+         * @param  string $file
+         * @return void
+         */
+        self::$includeFile = static function($file) {
+            include $file;
+        };
+    }
 }
diff --git a/tests/Composer/Test/Autoload/ClassLoaderTest.php b/tests/Composer/Test/Autoload/ClassLoaderTest.php
index 73e3b321d..96ba28c0c 100644
--- a/tests/Composer/Test/Autoload/ClassLoaderTest.php
+++ b/tests/Composer/Test/Autoload/ClassLoaderTest.php
@@ -59,4 +59,27 @@ class ClassLoaderTest extends TestCase
         $loader = new ClassLoader();
         $this->assertEmpty($loader->getPrefixes());
     }
+
+    public function testSerializability(): void
+    {
+        $loader = new ClassLoader();
+        $loader->add('Pearlike_', __DIR__ . '/Fixtures');
+        $loader->add('', __DIR__ . '/FALLBACK');
+        $loader->addPsr4('ShinyVendor\\ShinyPackage\\', __DIR__ . '/Fixtures');
+        $loader->addPsr4('', __DIR__ . '/FALLBACKPSR4');
+        $loader->addClassMap(['A' => '', 'B' => 'path']);
+        $loader->setApcuPrefix('prefix');
+        $loader->setClassMapAuthoritative(true);
+        $loader->setUseIncludePath(true);
+
+        $loader2 = unserialize(serialize($loader));
+        self::assertInstanceOf(ClassLoader::class, $loader2);
+        self::assertSame($loader->getApcuPrefix(), $loader2->getApcuPrefix());
+        self::assertSame($loader->getClassMap(), $loader2->getClassMap());
+        self::assertSame($loader->getFallbackDirs(), $loader2->getFallbackDirs());
+        self::assertSame($loader->getFallbackDirsPsr4(), $loader2->getFallbackDirsPsr4());
+        self::assertSame($loader->getPrefixes(), $loader2->getPrefixes());
+        self::assertSame($loader->getPrefixesPsr4(), $loader2->getPrefixesPsr4());
+        self::assertSame($loader->getUseIncludePath(), $loader2->getUseIncludePath());
+    }
 }