diff --git a/src/Symfony/Component/Debug/DebugClassLoader.php b/src/Symfony/Component/Debug/DebugClassLoader.php
index 2080944792f01..847cd009280ac 100644
--- a/src/Symfony/Component/Debug/DebugClassLoader.php
+++ b/src/Symfony/Component/Debug/DebugClassLoader.php
@@ -176,18 +176,30 @@ public function loadClass($class)
                 $class = substr($class, 1);
             }
 
-            $i = -1;
-            $tail = str_replace('\\', DIRECTORY_SEPARATOR, $class).'.php';
+            $i = 0;
+            $tail = DIRECTORY_SEPARATOR . str_replace('\\', DIRECTORY_SEPARATOR, $class).'.php';
             $len = strlen($tail);
 
             do {
-                $tail = substr($tail, $i+1);
-                $len -= $i+1;
-
-                if (! substr_compare($file, $tail, -$len, $len, true) && substr_compare($file, $tail, -$len, $len, false)) {
-                    throw new \RuntimeException(sprintf('Case mismatch between class and source file names: %s vs %s', $class, $file));
+                $tail = substr($tail, $i);
+                $len -= $i;
+
+                if (0 === substr_compare($file, $tail, -$len, $len, true)) {
+                    if (0 !== substr_compare($file, $tail, -$len, $len, false)) {
+                        if (method_exists($this->classLoader[0], 'getClassMap')) {
+                            $map = $this->classLoader[0]->getClassMap();
+                        } else {
+                            $map = array();
+                        }
+
+                        if (! isset($map[$class])) {
+                            throw new \RuntimeException(sprintf('Case mismatch between class and source file names: %s vs %s', $class, $file));
+                        }
+                    }
+
+                    break;
                 }
-            } while (false !== $i = strpos($tail, '\\'));
+            } while (false !== $i = strpos($tail, DIRECTORY_SEPARATOR, 1));
 
             if (! $exists) {
                 if (false !== strpos($class, '/')) {
diff --git a/src/Symfony/Component/Debug/Tests/DebugClassLoaderTest.php b/src/Symfony/Component/Debug/Tests/DebugClassLoaderTest.php
index 573869b63b60c..0c071414f7723 100644
--- a/src/Symfony/Component/Debug/Tests/DebugClassLoaderTest.php
+++ b/src/Symfony/Component/Debug/Tests/DebugClassLoaderTest.php
@@ -140,6 +140,24 @@ public function testFileCaseMismatch()
     {
         class_exists(__NAMESPACE__.'\Fixtures\CaseMismatch', true);
     }
+
+    /**
+     * @expectedException \RuntimeException
+     */
+    public function testPsr4CaseMismatch()
+    {
+        class_exists(__NAMESPACE__.'\Fixtures\Psr4CaseMismatch', true);
+    }
+
+    public function testNotPsr0()
+    {
+        $this->assertTrue(class_exists(__NAMESPACE__.'\Fixtures\NotPSR0', true));
+    }
+
+    public function testNotPsr0Bis()
+    {
+        $this->assertTrue(class_exists(__NAMESPACE__.'\Fixtures\NotPSR0bis', true));
+    }
 }
 
 class ClassLoader
@@ -148,6 +166,11 @@ public function loadClass($class)
     {
     }
 
+    public function getClassMap()
+    {
+        return array(__NAMESPACE__.'\Fixtures\NotPSR0bis' => __DIR__ . '/Fixtures/notPsr0Bis.php');
+    }
+
     public function findFile($class)
     {
         if (__NAMESPACE__.'\TestingUnsilencing' === $class) {
@@ -158,6 +181,12 @@ public function findFile($class)
             eval('namespace '.__NAMESPACE__.'; class TestingCaseMisMatch {}');
         } elseif (__NAMESPACE__.'\Fixtures\CaseMismatch' === $class) {
             return __DIR__ . '/Fixtures/casemismatch.php';
+        } elseif (__NAMESPACE__.'\Fixtures\Psr4CaseMismatch' === $class) {
+            return __DIR__ . '/Fixtures/psr4/Psr4CaseMismatch.php';
+        } elseif (__NAMESPACE__.'\Fixtures\NotPSR0' === $class) {
+            return __DIR__ . '/Fixtures/reallyNotPsr0.php';
+        } elseif (__NAMESPACE__.'\Fixtures\NotPSR0bis' === $class) {
+            return __DIR__ . '/Fixtures/notPsr0Bis.php';
         }
     }
 }
diff --git a/src/Symfony/Component/Debug/Tests/Fixtures/notPsr0Bis.php b/src/Symfony/Component/Debug/Tests/Fixtures/notPsr0Bis.php
new file mode 100644
index 0000000000000..4cf526719a6e6
--- /dev/null
+++ b/src/Symfony/Component/Debug/Tests/Fixtures/notPsr0Bis.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace Symfony\Component\Debug\Tests\Fixtures;
+
+class NotPSR0bis
+{
+}
diff --git a/src/Symfony/Component/Debug/Tests/Fixtures/psr4/Psr4CaseMismatch.php b/src/Symfony/Component/Debug/Tests/Fixtures/psr4/Psr4CaseMismatch.php
new file mode 100644
index 0000000000000..ec48dd22b4999
--- /dev/null
+++ b/src/Symfony/Component/Debug/Tests/Fixtures/psr4/Psr4CaseMismatch.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace Symfony\Component\Debug\Tests\Fixtures;
+
+class PSR4CaseMismatch
+{
+}
diff --git a/src/Symfony/Component/Debug/Tests/Fixtures/reallyNotPsr0.php b/src/Symfony/Component/Debug/Tests/Fixtures/reallyNotPsr0.php
new file mode 100644
index 0000000000000..8554725aa8b3b
--- /dev/null
+++ b/src/Symfony/Component/Debug/Tests/Fixtures/reallyNotPsr0.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace Symfony\Component\Debug\Tests\Fixtures;
+
+class NotPSR0
+{
+}