diff --git a/src/Composer/Autoload/AutoloadGenerator.php b/src/Composer/Autoload/AutoloadGenerator.php
index 3783bd22c..0de53a3bf 100644
--- a/src/Composer/Autoload/AutoloadGenerator.php
+++ b/src/Composer/Autoload/AutoloadGenerator.php
@@ -15,6 +15,7 @@ namespace Composer\Autoload;
 use Composer\Config;
 use Composer\EventDispatcher\EventDispatcher;
 use Composer\Installer\InstallationManager;
+use Composer\IO\IOInterface;
 use Composer\Package\AliasPackage;
 use Composer\Package\PackageInterface;
 use Composer\Repository\InstalledRepositoryInterface;
@@ -32,11 +33,17 @@ class AutoloadGenerator
      */
     private $eventDispatcher;
 
+    /**
+     * @var IOInterface
+     */
+    private $io;
+
     private $devMode = false;
 
-    public function __construct(EventDispatcher $eventDispatcher)
+    public function __construct(EventDispatcher $eventDispatcher, IOInterface $io=null)
     {
         $this->eventDispatcher = $eventDispatcher;
+        $this->io = $io;
     }
 
     public function setDevMode($devMode = true)
@@ -197,6 +204,12 @@ EOF;
             }
         }
 
+        if ($this->io && count(ClassMapGenerator::$ambiguousReferences) > 0) {
+            foreach (ClassMapGenerator::$ambiguousReferences as $ambiguousReference) {
+                $this->io->write('<info>Warning: Ambiguous class "'.$ambiguousReference['class'].'" resolution; defined in "'.$ambiguousReference[0].'" and in "'.$ambiguousReference[1].'" files.</info>');
+            }
+        }
+
         ksort($classMap);
         foreach ($classMap as $class => $code) {
             $classmapFile .= '    '.var_export($class, true).' => '.$code;
diff --git a/src/Composer/Autoload/ClassMapGenerator.php b/src/Composer/Autoload/ClassMapGenerator.php
index 1f20274e2..4805e7308 100644
--- a/src/Composer/Autoload/ClassMapGenerator.php
+++ b/src/Composer/Autoload/ClassMapGenerator.php
@@ -21,6 +21,12 @@ use Symfony\Component\Finder\Finder;
  */
 class ClassMapGenerator
 {
+
+    /**
+     * @var array
+     */
+    public static $ambiguousReferences = array();
+
     /**
      * Generate a class map file
      *
@@ -79,6 +85,14 @@ class ClassMapGenerator
             $classes = self::findClasses($filePath);
 
             foreach ($classes as $class) {
+                if (array_key_exists($class, $map)) {
+                    self::$ambiguousReferences[] = array(
+                        'class' => $class,
+                        '0' => $map[$class],
+                        '1' => $filePath
+                    );
+                }
+
                 $map[$class] = $filePath;
             }
         }
diff --git a/src/Composer/Factory.php b/src/Composer/Factory.php
index d0cd68b79..88fc4132e 100644
--- a/src/Composer/Factory.php
+++ b/src/Composer/Factory.php
@@ -253,7 +253,7 @@ class Factory
         $composer->setEventDispatcher($dispatcher);
 
         // initialize autoload generator
-        $generator = new AutoloadGenerator($dispatcher);
+        $generator = new AutoloadGenerator($dispatcher, $io);
         $composer->setAutoloadGenerator($generator);
 
         // add installers to the manager
diff --git a/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php b/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
index ddadc89c5..6b5049830 100644
--- a/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
+++ b/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
@@ -12,6 +12,7 @@
 namespace Composer\Test\Autoload;
 
 use Composer\Autoload\ClassMapGenerator;
+use Symfony\Component\Finder\Finder;
 
 class ClassMapGeneratorTest extends \PHPUnit_Framework_TestCase
 {
@@ -78,11 +79,9 @@ class ClassMapGeneratorTest extends \PHPUnit_Framework_TestCase
 
     public function testCreateMapFinderSupport()
     {
-        if (!class_exists('Symfony\\Component\\Finder\\Finder')) {
-            $this->markTestSkipped('Finder component is not available');
-        }
+        $this->checkIfFinderIsAvailable();
 
-        $finder = new \Symfony\Component\Finder\Finder();
+        $finder = new Finder();
         $finder->files()->in(__DIR__ . '/Fixtures/beta/NamespaceCollision');
 
         $this->assertEqualsNormalized(array(
@@ -103,6 +102,18 @@ class ClassMapGeneratorTest extends \PHPUnit_Framework_TestCase
 
         $find->invoke(null, __DIR__.'/no-file');
     }
+    public function testAmbiguousReference()
+    {
+        $this->checkIfFinderIsAvailable();
+
+        $finder = new Finder();
+        $finder->files()->in(__DIR__ . '/Fixtures/Ambiguous');
+
+        ClassMapGenerator::createMap($finder);
+
+        $this->assertEquals(1, count(ClassMapGenerator::$ambiguousReferences));
+        $this->assertEquals('A', ClassMapGenerator::$ambiguousReferences[0]['class']);
+    }
 
     /**
      * @expectedException \RuntimeException
@@ -123,4 +134,11 @@ class ClassMapGeneratorTest extends \PHPUnit_Framework_TestCase
         }
         $this->assertEquals($expected, $actual, $message);
     }
+
+    private function checkIfFinderIsAvailable()
+    {
+        if (!class_exists('Symfony\\Component\\Finder\\Finder')) {
+            $this->markTestSkipped('Finder component is not available');
+        }
+    }
 }
diff --git a/tests/Composer/Test/Autoload/Fixtures/Ambiguous/A.php b/tests/Composer/Test/Autoload/Fixtures/Ambiguous/A.php
new file mode 100644
index 000000000..ee9325efa
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/Ambiguous/A.php
@@ -0,0 +1,6 @@
+<?php
+
+class A
+{
+	
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/Ambiguous/other/A.php b/tests/Composer/Test/Autoload/Fixtures/Ambiguous/other/A.php
new file mode 100644
index 000000000..ee9325efa
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/Ambiguous/other/A.php
@@ -0,0 +1,6 @@
+<?php
+
+class A
+{
+	
+}