diff --git a/RouteDescriber/FosRestDescriber.php b/RouteDescriber/FosRestDescriber.php
index fd92f84..626f6a7 100644
--- a/RouteDescriber/FosRestDescriber.php
+++ b/RouteDescriber/FosRestDescriber.php
@@ -107,10 +107,12 @@ final class FosRestDescriber implements RouteDescriberInterface
         if ($requirements instanceof Constraint && !$requirements instanceof Regex) {
             if ($requirements instanceof DateTime) {
                 // As defined per RFC3339
-                if ('Y-m-d\TH:i:s' === $requirements->format || 'c' === $requirements->format) {
+                if (\DateTimeInterface::RFC3339 === $requirements->format || 'c' === $requirements->format) {
                     return 'date-time';
                 } elseif ('Y-m-d' === $requirements->format) {
                     return 'date';
+                } else {
+                    return null;
                 }
             }
 
diff --git a/Tests/Functional/Controller/FOSRestController.php b/Tests/Functional/Controller/FOSRestController.php
index 2857f28..772af46 100644
--- a/Tests/Functional/Controller/FOSRestController.php
+++ b/Tests/Functional/Controller/FOSRestController.php
@@ -29,8 +29,9 @@ class FOSRestController
      * @QueryParam(name="mapped", map=true)
      * @RequestParam(name="Barraa", key="bar", requirements="\d+")
      * @RequestParam(name="baz", requirements=@IsTrue)
-     * @RequestParam(name="datetime", requirements=@DateTime("Y-m-d\TH:i:s"))
+     * @RequestParam(name="datetime", requirements=@DateTime("Y-m-d\TH:i:sP"))
      * @RequestParam(name="datetimeAlt", requirements=@DateTime("c"))
+     * @RequestParam(name="datetimeNoFormat", requirements=@DateTime())
      * @RequestParam(name="date", requirements=@DateTime("Y-m-d"))
      */
     public function fosrestAction()
diff --git a/Tests/Functional/FOSRestTest.php b/Tests/Functional/FOSRestTest.php
index 8024011..66917b8 100644
--- a/Tests/Functional/FOSRestTest.php
+++ b/Tests/Functional/FOSRestTest.php
@@ -56,6 +56,9 @@ class FOSRestTest extends WebTestCase
         $dateTimeAltProperty = $this->getProperty($bodySchema, 'datetimeAlt');
         $this->assertEquals('date-time', $dateTimeAltProperty->format);
 
+        $dateTimeNoFormatProperty = $this->getProperty($bodySchema, 'datetimeNoFormat');
+        $this->assertEquals(OA\UNDEFINED, $dateTimeNoFormatProperty->format);
+
         $dateProperty = $this->getProperty($bodySchema, 'date');
         $this->assertEquals('date', $dateProperty->format);