diff --git a/src/Symfony/Bundle/FrameworkBundle/Test/KernelTestCase.php b/src/Symfony/Bundle/FrameworkBundle/Test/KernelTestCase.php
index b8ec208c1dbe4..26781cdf2285c 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Test/KernelTestCase.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Test/KernelTestCase.php
@@ -106,6 +106,14 @@ private static function getPhpUnitCliConfigArgument()
      */
     protected static function getKernelClass()
     {
+        if (isset($_SERVER['KERNEL_CLASS'])) {
+            if (!class_exists($class = $_SERVER['KERNEL_CLASS'])) {
+                throw new \RuntimeException(sprintf('Class "%s" doesn\'t exist or cannot be autoloaded. Check that the KERNEL_CLASS value in phpunit.xml matches the fully-qualified class name of your Kernel or override the %s::createKernel() method.', $class, static::class));
+            }
+
+            return $class;
+        }
+
         if (isset($_SERVER['KERNEL_DIR'])) {
             $dir = $_SERVER['KERNEL_DIR'];