diff --git a/lib/Doctrine/ORM/Persisters/SqlExpressionVisitor.php b/lib/Doctrine/ORM/Persisters/SqlExpressionVisitor.php
index b06358a20..7736943c6 100644
--- a/lib/Doctrine/ORM/Persisters/SqlExpressionVisitor.php
+++ b/lib/Doctrine/ORM/Persisters/SqlExpressionVisitor.php
@@ -66,6 +66,7 @@ class SqlExpressionVisitor extends ExpressionVisitor
         $value = $comparison->getValue()->getValue(); // shortcut for walkValue()
 
         if (isset($this->classMetadata->associationMappings[$field]) &&
+            $value !== null &&
             ! is_object($value) &&
             ! in_array($comparison->getOperator(), array(Comparison::IN, Comparison::NIN))) {
 
diff --git a/tests/Doctrine/Tests/ORM/Functional/EntityRepositoryTest.php b/tests/Doctrine/Tests/ORM/Functional/EntityRepositoryTest.php
index 517ff3d97..6432c3072 100644
--- a/tests/Doctrine/Tests/ORM/Functional/EntityRepositoryTest.php
+++ b/tests/Doctrine/Tests/ORM/Functional/EntityRepositoryTest.php
@@ -842,6 +842,35 @@ class EntityRepositoryTest extends \Doctrine\Tests\OrmFunctionalTestCase
         $this->assertEquals(2, count($users));
     }
 
+    /**
+     * @group DDC-2478
+     */
+    public function testMatchingCriteriaNullAssocComparison()
+    {
+        $fixtures       = $this->loadFixtureUserEmail();
+        $user           = $this->_em->merge($fixtures[0]);
+        $repository     = $this->_em->getRepository('Doctrine\Tests\Models\CMS\CmsUser');
+        $criteriaIsNull = Criteria::create()->where(Criteria::expr()->isNull('email'));
+        $criteriaEqNull = Criteria::create()->where(Criteria::expr()->eq('email', null));
+
+        $user->setEmail(null);
+        $this->_em->persist($user);
+        $this->_em->flush();
+        $this->_em->clear();
+
+        $usersIsNull = $repository->matching($criteriaIsNull);
+        $usersEqNull = $repository->matching($criteriaEqNull);
+
+        $this->assertCount(1, $usersIsNull);
+        $this->assertCount(1, $usersEqNull);
+
+        $this->assertInstanceOf('Doctrine\Tests\Models\CMS\CmsUser', $usersIsNull[0]);
+        $this->assertInstanceOf('Doctrine\Tests\Models\CMS\CmsUser', $usersEqNull[0]);
+
+        $this->assertNull($usersIsNull[0]->getEmail());
+        $this->assertNull($usersEqNull[0]->getEmail());
+    }
+
     /**
      * @group DDC-2055
      */