diff --git a/src/Composer/InstalledVersions.php b/src/Composer/InstalledVersions.php
index 81f4a6227..2c6c06f70 100644
--- a/src/Composer/InstalledVersions.php
+++ b/src/Composer/InstalledVersions.php
@@ -24,15 +24,10 @@ use Composer\Semver\VersionParser;
  */
 class InstalledVersions
 {
-    private static $installed = array();
+    private static $installed;
     private static $canGetVendors;
     private static $installedByVendor = array();
 
-    /**
-     * Initialize $installed array
-     */
-    public static function initializeInstalled() {}
-
     /**
      * Returns a list of all package names which are present, either by being installed, replaced or provided
      *
@@ -253,6 +248,10 @@ class InstalledVersions
     {
         @trigger_error('getRawData only returns the first dataset loaded, which may not be what you expect. Use getAllRawData() instead which returns all datasets for all autoloaders present in the process.', E_USER_DEPRECATED);
 
+        if (null === self::$installed) {
+            self::$installed = include __DIR__ . '/installed.php';
+        }
+
         return self::$installed;
     }
 
@@ -260,7 +259,7 @@ class InstalledVersions
      * Returns the raw data of all installed.php which are currently loaded for custom implementations
      *
      * @return array[]
-     * @psalm-return list<array{root: array{name: string, version: string, reference: string, pretty_version: string, aliases: string[]}, versions: array<string, array{pretty_version?: string, version?: string, aliases?: string[], reference?: string, replaced?: string[], provided?: string[]}>}>
+     * @psalm-return list<array{root: array{name: string, version: string, reference: string, pretty_version: string, aliases: string[], install_path: string}, versions: array<string, array{dev_requirement: bool, pretty_version?: string, version?: string, aliases?: string[], reference?: string, replaced?: string[], provided?: string[], install_path?: string}>}>
      */
     public static function getAllRawData()
     {
@@ -309,14 +308,18 @@ class InstalledVersions
                     $installed[] = self::$installedByVendor[$vendorDir];
                 } elseif (is_file($vendorDir.'/composer/installed.php')) {
                     $installed[] = self::$installedByVendor[$vendorDir] = require $vendorDir.'/composer/installed.php';
+                    if (null === self::$installed && strtr($vendorDir.'/composer', '\\', '/') === strtr(__DIR__, '\\', '/')) {
+                        self::$installed = $installed[count($installed) - 1];
+                    }
                 }
             }
         }
 
+        if (null === self::$installed) {
+            self::$installed = require __DIR__ . '/installed.php';
+        }
         $installed[] = self::$installed;
 
         return $installed;
     }
 }
-
-InstalledVersions::initializeInstalled();
diff --git a/src/Composer/Repository/FilesystemRepository.php b/src/Composer/Repository/FilesystemRepository.php
index 6b44d97d9..a80777033 100644
--- a/src/Composer/Repository/FilesystemRepository.php
+++ b/src/Composer/Repository/FilesystemRepository.php
@@ -130,14 +130,9 @@ class FilesystemRepository extends WritableArrayRepository
 
         if ($this->dumpVersions) {
             $versions = $this->generateInstalledVersions($installationManager, $installPaths, $devMode, $repoDir);
-            $versionsCode = $this->dumpToPhpCode($versions);
 
-            $fs->filePutContentsIfModified($repoDir.'/installed.php', '<?php return ' . $versionsCode . ';'."\n");
+            $fs->filePutContentsIfModified($repoDir.'/installed.php', '<?php return ' . $this->dumpToPhpCode($versions) . ';'."\n");
             $installedVersionsClass = file_get_contents(__DIR__.'/../InstalledVersions.php');
-            // while not strictly needed since https://github.com/composer/composer/pull/9635 - we keep this for BC
-            // and overall broader compatibility with people that may not use Composer's ClassLoader. They can
-            // simply include InstalledVersions.php manually and have it working in a basic way.
-            $installedVersionsClass = str_replace('public static function initializeInstalled() {}', 'public static function initializeInstalled() {' . PHP_EOL . 'self::$installed = ' . $versionsCode . ';' . PHP_EOL . '}', $installedVersionsClass);
             $fs->filePutContentsIfModified($repoDir.'/InstalledVersions.php', $installedVersionsClass);
 
             \Composer\InstalledVersions::reload($versions);