diff --git a/bin/composer-dependency-analyser b/bin/composer-dependency-analyser
index 459fba9..1093343 100755
--- a/bin/composer-dependency-analyser
+++ b/bin/composer-dependency-analyser
@@ -39,7 +39,7 @@ try {
     $configuration = $initializer->initConfiguration($options, $composerJson);
     $classLoaders = $initializer->initComposerClassLoaders();
 
-    $analyser = new Analyser($stopwatch, $classLoaders, $configuration, $composerJson->dependencies);
+    $analyser = new Analyser($stopwatch, $composerJson->composerVendorDir, $classLoaders, $configuration, $composerJson->dependencies);
     $result = $analyser->run();
 
     $formatter = $initializer->initFormatter($options);
diff --git a/src/Analyser.php b/src/Analyser.php
index 811d9a8..2c984bd 100644
--- a/src/Analyser.php
+++ b/src/Analyser.php
@@ -22,6 +22,7 @@
 use function array_filter;
 use function array_key_exists;
 use function array_keys;
+use function array_values;
 use function explode;
 use function file_get_contents;
 use function get_declared_classes;
@@ -50,9 +51,12 @@ class Analyser
     private $stopwatch;
 
     /**
-     * vendorDir => ClassLoader
-     *
-     * @var array<string, ClassLoader>
+     * @var list<string>
+     */
+    private $vendorDirs;
+
+    /**
+     * @var list<ClassLoader>
      */
     private $classLoaders;
 
@@ -95,6 +99,7 @@ class Analyser
      */
     public function __construct(
         Stopwatch $stopwatch,
+        string $defaultVendorDir,
         array $classLoaders,
         Configuration $config,
         array $composerJsonDependencies
@@ -103,7 +108,8 @@ public function __construct(
         $this->stopwatch = $stopwatch;
         $this->config = $config;
         $this->composerJsonDependencies = $composerJsonDependencies;
-        $this->classLoaders = $classLoaders;
+        $this->vendorDirs = array_keys($classLoaders + [$defaultVendorDir => null]);
+        $this->classLoaders = array_values($classLoaders);
 
         $this->initExistingSymbols();
     }
@@ -311,7 +317,7 @@ private function isDevDependency(string $packageName): bool
 
     private function getPackageNameFromVendorPath(string $realPath): string
     {
-        foreach ($this->classLoaders as $vendorDir => $_) {
+        foreach ($this->vendorDirs as $vendorDir) {
             if (strpos($realPath, $vendorDir) === 0) {
                 $filePathInVendor = trim(str_replace($vendorDir, '', $realPath), DIRECTORY_SEPARATOR);
                 [$vendor, $package] = explode(DIRECTORY_SEPARATOR, $filePathInVendor, 3);
@@ -366,7 +372,7 @@ private function listPhpFilesIn(string $path): Generator
 
     private function isVendorPath(string $realPath): bool
     {
-        foreach ($this->classLoaders as $vendorDir => $_) {
+        foreach ($this->vendorDirs as $vendorDir) {
             if (strpos($realPath, $vendorDir) === 0) {
                 return true;
             }
diff --git a/src/ComposerJson.php b/src/ComposerJson.php
index c43dc27..6280556 100644
--- a/src/ComposerJson.php
+++ b/src/ComposerJson.php
@@ -31,6 +31,12 @@
 class ComposerJson
 {
 
+    /**
+     * @readonly
+     * @var string
+     */
+    public $composerVendorDir;
+
     /**
      * @readonly
      * @var string
@@ -72,7 +78,8 @@ public function __construct(
         $basePath = dirname($composerJsonPath);
 
         $composerJsonData = $this->parseComposerJson($composerJsonPath);
-        $this->composerAutoloadPath = $this->resolveComposerAutoloadPath($basePath, $composerJsonData['config']['vendor-dir'] ?? 'vendor');
+        $this->composerVendorDir = $this->resolveComposerVendorDir($basePath, $composerJsonData['config']['vendor-dir'] ?? 'vendor');
+        $this->composerAutoloadPath = Path::normalize($this->composerVendorDir . '/autoload.php');
 
         $requiredPackages = $composerJsonData['require'] ?? [];
         $requiredDevPackages = $composerJsonData['require-dev'] ?? [];
@@ -261,13 +268,13 @@ private function parseComposerJson(string $composerJsonPath): array
         return $composerJsonData; // @phpstan-ignore-line ignore mixed returned
     }
 
-    private function resolveComposerAutoloadPath(string $basePath, string $vendorDir): string
+    private function resolveComposerVendorDir(string $basePath, string $vendorDir): string
     {
         if (Path::isAbsolute($vendorDir)) {
-            return Path::normalize($vendorDir . '/autoload.php');
+            return Path::normalize($vendorDir);
         }
 
-        return Path::normalize($basePath . '/' . $vendorDir . '/autoload.php');
+        return Path::normalize($basePath . '/' . $vendorDir);
     }
 
 }
diff --git a/tests/AnalyserTest.php b/tests/AnalyserTest.php
index 720de96..0f6ed15 100644
--- a/tests/AnalyserTest.php
+++ b/tests/AnalyserTest.php
@@ -45,6 +45,7 @@ public function test(callable $editConfig, AnalysisResult $expectedResult): void
 
         $detector = new Analyser(
             $this->getStopwatchMock(),
+            $vendorDir,
             [$vendorDir => $this->getClassLoaderMock()],
             $config,
             $dependencies
@@ -477,12 +478,14 @@ public function testNativeTypesNotReported(): void
         $path = realpath(__DIR__ . '/data/not-autoloaded/builtin/native-symbols.php');
         self::assertNotFalse($path);
 
+        $vendorDir = __DIR__;
         $config = new Configuration();
         $config->addPathToScan($path, false);
 
         $detector = new Analyser(
             $this->getStopwatchMock(),
-            [__DIR__ => $this->getClassLoaderMock()],
+            $vendorDir,
+            [$vendorDir => $this->getClassLoaderMock()],
             $config,
             []
         );
@@ -503,13 +506,16 @@ public function testNoMultipleScansOfTheSameFile(): void
         $path = realpath(__DIR__ . '/data/not-autoloaded/analysis/unknown-classes.php');
         self::assertNotFalse($path);
 
+        $vendorDir = __DIR__ . '/data/autoloaded/vendor';
+
         $config = new Configuration();
         $config->addPathToScan($path, true);
         $config->addPathToScan($path, true);
 
         $detector = new Analyser(
             $this->getStopwatchMock(),
-            [__DIR__ . '/data/autoloaded/vendor' => $this->getClassLoaderMock()],
+            $vendorDir,
+            [$vendorDir => $this->getClassLoaderMock()],
             $config,
             []
         );
@@ -538,6 +544,7 @@ public function testDevPathInsideProdPath(): void
 
         $detector = new Analyser(
             $this->getStopwatchMock(),
+            $vendorDir,
             [$vendorDir => $this->getClassLoaderMock()],
             $config,
             [
@@ -565,6 +572,7 @@ public function testProdPathInsideDevPath(): void
 
         $detector = new Analyser(
             $this->getStopwatchMock(),
+            $vendorDir,
             [$vendorDir => $this->getClassLoaderMock()],
             $config,
             [
@@ -591,6 +599,7 @@ public function testOtherSymbols(): void
 
         $detector = new Analyser(
             $this->getStopwatchMock(),
+            $vendorDir,
             [$vendorDir => $this->getClassLoaderMock()],
             $config,
             []
@@ -626,6 +635,7 @@ public function testPharSupport(): void
 
         $detector = new Analyser(
             $this->getStopwatchMock(),
+            $vendorDir,
             [$vendorDir => $this->getClassLoaderMock()],
             $config,
             [
@@ -665,6 +675,7 @@ public function testMultipleClassloaders(): void
 
         $detector = new Analyser(
             $this->getStopwatchMock(),
+            $vendorDir,
             $classLoaders,
             $config,
             [
@@ -692,6 +703,7 @@ public function testFunctions(): void
 
         $detector = new Analyser(
             $this->getStopwatchMock(),
+            $vendorDir,
             [$vendorDir => $this->getClassLoaderMock()],
             $config,
             ['org/package' => false]
@@ -713,6 +725,7 @@ public function testExplicitFileWithoutExtension(): void
 
         $detector = new Analyser(
             $this->getStopwatchMock(),
+            $vendorDir,
             [$vendorDir => $this->getClassLoaderMock()],
             $config,
             [