diff --git a/src/Symfony/Component/Routing/Generator/UrlGenerator.php b/src/Symfony/Component/Routing/Generator/UrlGenerator.php
index 91794423234fe..fbb5cca0b0a0f 100644
--- a/src/Symfony/Component/Routing/Generator/UrlGenerator.php
+++ b/src/Symfony/Component/Routing/Generator/UrlGenerator.php
@@ -156,21 +156,26 @@ protected function doGenerate($variables, $defaults, $requirements, $tokens, $pa
         $message = 'Parameter "{parameter}" for route "{route}" must match "{expected}" ("{given}" given) to generate a corresponding URL.';
         foreach ($tokens as $token) {
             if ('variable' === $token[0]) {
-                if (!$optional || !array_key_exists($token[3], $defaults) || null !== $mergedParams[$token[3]] && (string) $mergedParams[$token[3]] !== (string) $defaults[$token[3]]) {
+                $varName = $token[3];
+                if ($important = ('!' === $varName[0])) {
+                    $varName = substr($varName, 1);
+                }
+
+                if (!$optional || $important || !array_key_exists($varName, $defaults) || (null !== $mergedParams[$varName] && (string) $mergedParams[$varName] !== (string) $defaults[$varName])) {
                     // check requirement
-                    if (null !== $this->strictRequirements && !preg_match('#^'.$token[2].'$#'.(empty($token[4]) ? '' : 'u'), $mergedParams[$token[3]])) {
+                    if (null !== $this->strictRequirements && !preg_match('#^'.$token[2].'$#'.(empty($token[4]) ? '' : 'u'), $mergedParams[$varName])) {
                         if ($this->strictRequirements) {
-                            throw new InvalidParameterException(strtr($message, array('{parameter}' => $token[3], '{route}' => $name, '{expected}' => $token[2], '{given}' => $mergedParams[$token[3]])));
+                            throw new InvalidParameterException(strtr($message, array('{parameter}' => $varName, '{route}' => $name, '{expected}' => $token[2], '{given}' => $mergedParams[$varName])));
                         }
 
                         if ($this->logger) {
-                            $this->logger->error($message, array('parameter' => $token[3], 'route' => $name, 'expected' => $token[2], 'given' => $mergedParams[$token[3]]));
+                            $this->logger->error($message, array('parameter' => $varName, 'route' => $name, 'expected' => $token[2], 'given' => $mergedParams[$varName]));
                         }
 
                         return;
                     }
 
-                    $url = $token[1].$mergedParams[$token[3]].$url;
+                    $url = $token[1].$mergedParams[$varName].$url;
                     $optional = false;
                 }
             } else {
diff --git a/src/Symfony/Component/Routing/RouteCompiler.php b/src/Symfony/Component/Routing/RouteCompiler.php
index 66b291b831adc..abab86be7a95b 100644
--- a/src/Symfony/Component/Routing/RouteCompiler.php
+++ b/src/Symfony/Component/Routing/RouteCompiler.php
@@ -111,7 +111,7 @@ private static function compilePattern(Route $route, $pattern, $isHost)
 
         // Match all variables enclosed in "{}" and iterate over them. But we only want to match the innermost variable
         // in case of nested "{}", e.g. {foo{bar}}. This in ensured because \w does not match "{" or "}" itself.
-        preg_match_all('#\{\w+\}#', $pattern, $matches, PREG_OFFSET_CAPTURE | PREG_SET_ORDER);
+        preg_match_all('#\{!?\w+\}#', $pattern, $matches, PREG_OFFSET_CAPTURE | PREG_SET_ORDER);
         foreach ($matches as $match) {
             $varName = substr($match[0][0], 1, -1);
             // get all static text preceding the current variable
@@ -184,6 +184,9 @@ private static function compilePattern(Route $route, $pattern, $isHost)
             }
 
             $tokens[] = array('variable', $isSeparator ? $precedingChar : '', $regexp, $varName);
+            if ('!' === $varName[0]) {
+                $varName = substr($varName, 1);
+            }
             $variables[] = $varName;
         }
 
@@ -283,6 +286,10 @@ private static function computeRegexp(array $tokens, int $index, int $firstOptio
             // Text tokens
             return preg_quote($token[1], self::REGEX_DELIMITER);
         } else {
+            if ('variable' === $token[0] && '!' === $token[3][0]) {
+                $token[3] = substr($token[3], 1);
+            }
+
             // Variable tokens
             if (0 === $index && 0 === $firstOptional) {
                 // When the only token is an optional variable token, the separator is required
diff --git a/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php b/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php
index d4bf18ccac929..bb248d0fcd997 100644
--- a/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php
+++ b/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php
@@ -397,6 +397,27 @@ public function testDefaultRequirementOfVariable()
         $this->assertSame('/app.php/index.mobile.html', $generator->generate('test', array('page' => 'index', '_format' => 'mobile.html')));
     }
 
+    public function testImportantVariable()
+    {
+        $routes = $this->getRoutes('test', (new Route('/{page}.{!_format}'))->addDefaults(array('_format' => 'mobile.html')));
+        $generator = $this->getGenerator($routes);
+
+        $this->assertSame('/app.php/index.xml', $generator->generate('test', array('page' => 'index', '_format' => 'xml')));
+        $this->assertSame('/app.php/index.mobile.html', $generator->generate('test', array('page' => 'index', '_format' => 'mobile.html')));
+        $this->assertSame('/app.php/index.mobile.html', $generator->generate('test', array('page' => 'index')));
+    }
+
+    /**
+     * @expectedException \Symfony\Component\Routing\Exception\MissingMandatoryParametersException
+     */
+    public function testImportantVariableWithNoDefault()
+    {
+        $routes = $this->getRoutes('test', new Route('/{page}.{!_format}'));
+        $generator = $this->getGenerator($routes);
+
+        $generator->generate('test', array('page' => 'index'));
+    }
+
     /**
      * @expectedException \Symfony\Component\Routing\Exception\InvalidParameterException
      */
diff --git a/src/Symfony/Component/Routing/Tests/Matcher/UrlMatcherTest.php b/src/Symfony/Component/Routing/Tests/Matcher/UrlMatcherTest.php
index bcaf3dee7218a..ecf6c5926bc5c 100644
--- a/src/Symfony/Component/Routing/Tests/Matcher/UrlMatcherTest.php
+++ b/src/Symfony/Component/Routing/Tests/Matcher/UrlMatcherTest.php
@@ -177,6 +177,15 @@ public function testMatchSpecialRouteName()
         $this->assertEquals(array('_route' => '$péß^a|'), $matcher->match('/bar'));
     }
 
+    public function testMatchImportantVariable()
+    {
+        $collection = new RouteCollection();
+        $collection->add('index', new Route('/index.{!_format}', array('_format' => 'xml')));
+
+        $matcher = $this->getUrlMatcher($collection);
+        $this->assertEquals(array('_route' => 'index', '_format' => 'xml'), $matcher->match('/index.xml'));
+    }
+
     /**
      * @expectedException \Symfony\Component\Routing\Exception\ResourceNotFoundException
      */