diff --git a/src/Composer/Autoload/AutoloadGenerator.php b/src/Composer/Autoload/AutoloadGenerator.php
index 38e44ca2a..59addd0b4 100644
--- a/src/Composer/Autoload/AutoloadGenerator.php
+++ b/src/Composer/Autoload/AutoloadGenerator.php
@@ -115,12 +115,14 @@ EOF;
         $namespacesFile .= ");\n";
 
         if (isset($autoloads['classmap'])) {
-            $it = new \RecursiveIteratorIterator(new \RecursiveArrayIterator($autoloads['classmap']));
-            ClassMapGenerator::dump(iterator_to_array($it), $targetDir.'/autoload_classmap.php');
+            // flatten array
+            $autoloads['classmap'] = new \RecursiveIteratorIterator(new \RecursiveArrayIterator($autoloads['classmap']));
         } else {
-            file_put_contents($targetDir.'/autoload_classmap.php', '<?php return array();');
+            $autoloads['classmap'] = array();
         }
 
+        ClassMapGenerator::dump($autoloads['classmap'], $targetDir.'/autoload_classmap.php');
+
         file_put_contents($targetDir.'/autoload.php', $autoloadFile);
         file_put_contents($targetDir.'/autoload_namespaces.php', $namespacesFile);
         copy(__DIR__.'/ClassLoader.php', $targetDir.'/ClassLoader.php');
diff --git a/src/Composer/Autoload/ClassMapGenerator.php b/src/Composer/Autoload/ClassMapGenerator.php
index dad422929..c9fa687d6 100644
--- a/src/Composer/Autoload/ClassMapGenerator.php
+++ b/src/Composer/Autoload/ClassMapGenerator.php
@@ -23,12 +23,11 @@ class ClassMapGenerator
     /**
      * Generate a class map file
      *
-     * @param array|string $dirs Directories or a single path to search in
+     * @param Traversable $dirs Directories or a single path to search in
      * @param string $file The name of the class map file
      */
     static public function dump($dirs, $file)
     {
-        $dirs = (array) $dirs;
         $maps = array();
 
         foreach ($dirs as $dir) {
diff --git a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
index f8e188906..cff5a5834 100644
--- a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
+++ b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
@@ -134,6 +134,40 @@ class AutoloadGeneratorTest extends TestCase
         mkdir($this->vendorDir.'/.composer', 0777, true);
         $this->generator->dump($this->repository, $package, $this->im, $this->vendorDir.'/.composer');
         $this->assertAutoloadFiles('vendors', $this->vendorDir.'/.composer');
+        $this->assertTrue(file_exists($this->vendorDir.'/.composer/autoload_classmap.php'), "ClassMap file needs to be generated, even if empty.");
+    }
+
+    public function testVendorsClassMapAutoloading()
+    {
+        $package = new MemoryPackage('a', '1.0', '1.0');
+
+        $packages = array();
+        $packages[] = $a = new MemoryPackage('a/a', '1.0', '1.0');
+        $packages[] = $b = new MemoryPackage('b/b', '1.0', '1.0');
+        $a->setAutoload(array('classmap' => array('src/')));
+        $b->setAutoload(array('classmap' => array('src/', 'lib/')));
+
+        $this->repository->expects($this->once())
+            ->method('getPackages')
+            ->will($this->returnValue($packages));
+
+        @mkdir($this->vendorDir.'/.composer', 0777, true);
+        mkdir($this->vendorDir.'/a/a/src', 0777, true);
+        mkdir($this->vendorDir.'/b/b/src', 0777, true);
+        mkdir($this->vendorDir.'/b/b/lib', 0777, true);
+        file_put_contents($this->vendorDir.'/a/a/src/a.php', '<?php class ClassMapFoo {}');
+        file_put_contents($this->vendorDir.'/b/b/src/b.php', '<?php class ClassMapBar {}');
+        file_put_contents($this->vendorDir.'/b/b/lib/c.php', '<?php class ClassMapBaz {}');
+
+        $this->generator->dump($this->repository, $package, $this->im, $this->vendorDir.'/.composer');
+        $this->assertTrue(file_exists($this->vendorDir.'/.composer/autoload_classmap.php'), "ClassMap file needs to be generated, even if empty.");
+        $this->assertEquals(array(
+                'ClassMapFoo' => $this->vendorDir.'/a/a/src/a.php',
+                'ClassMapBar' => $this->vendorDir.'/b/b/src/b.php',
+                'ClassMapBaz' => $this->vendorDir.'/b/b/lib/c.php',
+            ),
+            include ($this->vendorDir.'/.composer/autoload_classmap.php')
+        );
     }
 
     public function testOverrideVendorsAutoloading()
diff --git a/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php b/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
new file mode 100644
index 000000000..d40321768
--- /dev/null
+++ b/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
@@ -0,0 +1,83 @@
+<?php
+
+/*
+ * This file was copied from the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Composer\Test\Autoload;
+
+use Composer\Autoload\ClassMapGenerator;
+
+class ClassMapGeneratorTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @dataProvider getTestCreateMapTests
+     */
+    public function testCreateMap($directory, $expected)
+    {
+        $this->assertEqualsNormalized($expected, ClassMapGenerator::createMap($directory));
+    }
+
+    public function getTestCreateMapTests()
+    {
+        return array(
+            array(__DIR__.'/Fixtures/Namespaced', array(
+                'Namespaced\\Bar' => realpath(__DIR__).'/Fixtures/Namespaced/Bar.php',
+                'Namespaced\\Foo' => realpath(__DIR__).'/Fixtures/Namespaced/Foo.php',
+                'Namespaced\\Baz' => realpath(__DIR__).'/Fixtures/Namespaced/Baz.php',
+                )
+            ),
+            array(__DIR__.'/Fixtures/beta/NamespaceCollision', array(
+                'NamespaceCollision\\A\\B\\Bar' => realpath(__DIR__).'/Fixtures/beta/NamespaceCollision/A/B/Bar.php',
+                'NamespaceCollision\\A\\B\\Foo' => realpath(__DIR__).'/Fixtures/beta/NamespaceCollision/A/B/Foo.php',
+            )),
+            array(__DIR__.'/Fixtures/Pearlike', array(
+                'Pearlike_Foo' => realpath(__DIR__).'/Fixtures/Pearlike/Foo.php',
+                'Pearlike_Bar' => realpath(__DIR__).'/Fixtures/Pearlike/Bar.php',
+                'Pearlike_Baz' => realpath(__DIR__).'/Fixtures/Pearlike/Baz.php',
+            )),
+            array(__DIR__.'/Fixtures/classmap', array(
+                'Foo\\Bar\\A'             => realpath(__DIR__).'/Fixtures/classmap/sameNsMultipleClasses.php',
+                'Foo\\Bar\\B'             => realpath(__DIR__).'/Fixtures/classmap/sameNsMultipleClasses.php',
+                'Alpha\\A'                => realpath(__DIR__).'/Fixtures/classmap/multipleNs.php',
+                'Alpha\\B'                => realpath(__DIR__).'/Fixtures/classmap/multipleNs.php',
+                'Beta\\A'                 => realpath(__DIR__).'/Fixtures/classmap/multipleNs.php',
+                'Beta\\B'                 => realpath(__DIR__).'/Fixtures/classmap/multipleNs.php',
+                'ClassMap\\SomeInterface' => realpath(__DIR__).'/Fixtures/classmap/SomeInterface.php',
+                'ClassMap\\SomeParent'    => realpath(__DIR__).'/Fixtures/classmap/SomeParent.php',
+                'ClassMap\\SomeClass'     => realpath(__DIR__).'/Fixtures/classmap/SomeClass.php',
+            )),
+        );
+    }
+
+    public function testCreateMapFinderSupport()
+    {
+        if (!class_exists('Symfony\\Component\\Finder\\Finder')) {
+            $this->markTestSkipped('Finder component is not available');
+        }
+
+        $finder = new \Symfony\Component\Finder\Finder();
+        $finder->files()->in(__DIR__ . '/Fixtures/beta/NamespaceCollision');
+
+        $this->assertEqualsNormalized(array(
+            'NamespaceCollision\\A\\B\\Bar' => realpath(__DIR__).'/Fixtures/beta/NamespaceCollision/A/B/Bar.php',
+            'NamespaceCollision\\A\\B\\Foo' => realpath(__DIR__).'/Fixtures/beta/NamespaceCollision/A/B/Foo.php',
+        ), ClassMapGenerator::createMap($finder));
+    }
+
+    protected function assertEqualsNormalized($expected, $actual, $message = null)
+    {
+        foreach ($expected as $ns => $path) {
+            $expected[$ns] = strtr($path, '\\', '/');
+        }
+        foreach ($actual as $ns => $path) {
+            $actual[$ns] = strtr($path, '\\', '/');
+        }
+        $this->assertEquals($expected, $actual, $message);
+    }
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/Namespaced/Bar.php b/tests/Composer/Test/Autoload/Fixtures/Namespaced/Bar.php
new file mode 100644
index 000000000..f9c519a66
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/Namespaced/Bar.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Namespaced;
+
+class Bar
+{
+    public static $loaded = true;
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/Namespaced/Baz.php b/tests/Composer/Test/Autoload/Fixtures/Namespaced/Baz.php
new file mode 100644
index 000000000..c3723f0ee
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/Namespaced/Baz.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Namespaced;
+
+class Baz
+{
+    public static $loaded = true;
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/Namespaced/Foo.php b/tests/Composer/Test/Autoload/Fixtures/Namespaced/Foo.php
new file mode 100644
index 000000000..a3e0e0613
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/Namespaced/Foo.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Namespaced;
+
+class Foo
+{
+    public static $loaded = true;
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/Pearlike/Bar.php b/tests/Composer/Test/Autoload/Fixtures/Pearlike/Bar.php
new file mode 100644
index 000000000..63661695b
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/Pearlike/Bar.php
@@ -0,0 +1,6 @@
+<?php
+
+class Pearlike_Bar
+{
+    public static $loaded = true;
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/Pearlike/Baz.php b/tests/Composer/Test/Autoload/Fixtures/Pearlike/Baz.php
new file mode 100644
index 000000000..3aa836755
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/Pearlike/Baz.php
@@ -0,0 +1,6 @@
+<?php
+
+class Pearlike_Baz
+{
+    public static $loaded = true;
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/Pearlike/Foo.php b/tests/Composer/Test/Autoload/Fixtures/Pearlike/Foo.php
new file mode 100644
index 000000000..c51b1569c
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/Pearlike/Foo.php
@@ -0,0 +1,6 @@
+<?php
+
+class Pearlike_Foo
+{
+    public static $loaded = true;
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/beta/NamespaceCollision/A/B/Bar.php b/tests/Composer/Test/Autoload/Fixtures/beta/NamespaceCollision/A/B/Bar.php
new file mode 100644
index 000000000..6a4678832
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/beta/NamespaceCollision/A/B/Bar.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace NamespaceCollision\A\B;
+
+class Bar
+{
+    public static $loaded = true;
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/beta/NamespaceCollision/A/B/Foo.php b/tests/Composer/Test/Autoload/Fixtures/beta/NamespaceCollision/A/B/Foo.php
new file mode 100644
index 000000000..d3a43e8b8
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/beta/NamespaceCollision/A/B/Foo.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace NamespaceCollision\A\B;
+
+class Foo
+{
+    public static $loaded = true;
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/beta/PrefixCollision/A/B/Bar.php b/tests/Composer/Test/Autoload/Fixtures/beta/PrefixCollision/A/B/Bar.php
new file mode 100644
index 000000000..f2682e498
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/beta/PrefixCollision/A/B/Bar.php
@@ -0,0 +1,6 @@
+<?php
+
+class PrefixCollision_A_B_Bar
+{
+    public static $loaded = true;
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/beta/PrefixCollision/A/B/Foo.php b/tests/Composer/Test/Autoload/Fixtures/beta/PrefixCollision/A/B/Foo.php
new file mode 100644
index 000000000..af7ca7043
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/beta/PrefixCollision/A/B/Foo.php
@@ -0,0 +1,6 @@
+<?php
+
+class PrefixCollision_A_B_Foo
+{
+    public static $loaded = true;
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/classmap/SomeClass.php b/tests/Composer/Test/Autoload/Fixtures/classmap/SomeClass.php
new file mode 100644
index 000000000..869eabc30
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/classmap/SomeClass.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace ClassMap;
+
+class SomeClass extends SomeParent implements SomeInterface
+{
+
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/classmap/SomeInterface.php b/tests/Composer/Test/Autoload/Fixtures/classmap/SomeInterface.php
new file mode 100644
index 000000000..010ecc5c7
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/classmap/SomeInterface.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace ClassMap;
+
+interface SomeInterface
+{
+
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/classmap/SomeParent.php b/tests/Composer/Test/Autoload/Fixtures/classmap/SomeParent.php
new file mode 100644
index 000000000..817c03b66
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/classmap/SomeParent.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace ClassMap;
+
+abstract class SomeParent
+{
+
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/classmap/multipleNs.php b/tests/Composer/Test/Autoload/Fixtures/classmap/multipleNs.php
new file mode 100644
index 000000000..27f96f704
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/classmap/multipleNs.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace Alpha {
+    class A {}
+    class B {}
+}
+
+namespace Beta {
+    class A {}
+    class B {}
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/classmap/notAClass.php b/tests/Composer/Test/Autoload/Fixtures/classmap/notAClass.php
new file mode 100644
index 000000000..49eb3ff05
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/classmap/notAClass.php
@@ -0,0 +1,3 @@
+<?php
+
+$a = new stdClass();
diff --git a/tests/Composer/Test/Autoload/Fixtures/classmap/notPhpFile.md b/tests/Composer/Test/Autoload/Fixtures/classmap/notPhpFile.md
new file mode 100644
index 000000000..6e48e5a63
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/classmap/notPhpFile.md
@@ -0,0 +1 @@
+This file should be skipped.
diff --git a/tests/Composer/Test/Autoload/Fixtures/classmap/sameNsMultipleClasses.php b/tests/Composer/Test/Autoload/Fixtures/classmap/sameNsMultipleClasses.php
new file mode 100644
index 000000000..f92ae8be4
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/classmap/sameNsMultipleClasses.php
@@ -0,0 +1,6 @@
+<?php
+
+namespace Foo\Bar;
+
+class A {}
+class B {}