diff --git a/src/Symfony/Component/Routing/Generator/UrlGenerator.php b/src/Symfony/Component/Routing/Generator/UrlGenerator.php
index 2a6328ad3f8f6..942280acdb1c7 100644
--- a/src/Symfony/Component/Routing/Generator/UrlGenerator.php
+++ b/src/Symfony/Component/Routing/Generator/UrlGenerator.php
@@ -159,7 +159,7 @@ protected function doGenerate($variables, $defaults, $requirements, $tokens, $pa
         $optional = true;
         foreach ($tokens as $token) {
             if ('variable' === $token[0]) {
-                if (!$optional || !array_key_exists($token[3], $defaults) || (string) $mergedParams[$token[3]] !== (string) $defaults[$token[3]]) {
+                if (!$optional || !array_key_exists($token[3], $defaults) || null !== $mergedParams[$token[3]] && (string) $mergedParams[$token[3]] !== (string) $defaults[$token[3]]) {
                     // check requirement
                     if (null !== $this->strictRequirements && !preg_match('#^'.$token[2].'$#', $mergedParams[$token[3]])) {
                         $message = sprintf('Parameter "%s" for route "%s" must match "%s" ("%s" given) to generate a corresponding URL.', $token[3], $name, $token[2], $mergedParams[$token[3]]);
diff --git a/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php b/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php
index 0728503b0632c..b28fdd8279163 100644
--- a/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php
+++ b/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php
@@ -286,6 +286,13 @@ public function testWithAnIntegerAsADefaultValue()
         $this->assertEquals('/app.php/foo', $this->getGenerator($routes)->generate('test', array('default' => 'foo')));
     }
 
+    public function testNullForOptionalParameterIsIgnored()
+    {
+        $routes = $this->getRoutes('test', new Route('/test/{default}', array('default' => 0)));
+
+        $this->assertEquals('/app.php/test', $this->getGenerator($routes)->generate('test', array('default' => null)));
+    }
+
     public function testQueryParamSameAsDefault()
     {
         $routes = $this->getRoutes('test', new Route('/test', array('default' => 'value')));