diff --git a/lib/Doctrine/ORM/EntityManager.php b/lib/Doctrine/ORM/EntityManager.php
index 51d6dbf05..b61a2557b 100644
--- a/lib/Doctrine/ORM/EntityManager.php
+++ b/lib/Doctrine/ORM/EntityManager.php
@@ -19,6 +19,7 @@
 
 namespace Doctrine\ORM;
 
+use Doctrine\ORM\Mapping\MappingException;
 use Exception;
 use Doctrine\Common\EventManager;
 use Doctrine\DBAL\Connection;
@@ -539,10 +540,22 @@ use Doctrine\Common\Util\ClassUtils;
      * @param string|null $entityName if given, only entities of this type will get detached
      *
      * @return void
+     *
+     * @throws ORMInvalidArgumentException                           if a non-null non-string value is given
+     * @throws \Doctrine\Common\Persistence\Mapping\MappingException if a $entityName is given, but that entity is not
+     *                                                               found in the mappings
      */
     public function clear($entityName = null)
     {
-        $this->unitOfWork->clear($entityName);
+        if (null !== $entityName && ! is_string($entityName)) {
+            throw ORMInvalidArgumentException::invalidEntityName($entityName);
+        }
+
+        $this->unitOfWork->clear(
+            null === $entityName
+                ? null
+                : $this->metadataFactory->getMetadataFor($entityName)->getName()
+        );
     }
 
     /**
diff --git a/lib/Doctrine/ORM/ORMException.php b/lib/Doctrine/ORM/ORMException.php
index 919789d92..039ef2eaa 100644
--- a/lib/Doctrine/ORM/ORMException.php
+++ b/lib/Doctrine/ORM/ORMException.php
@@ -101,7 +101,7 @@ class ORMException extends Exception
         return new self("Unrecognized field: $field");
     }
 
-     /**
+    /**
      *
      * @param string $class
      * @param string $association
diff --git a/lib/Doctrine/ORM/ORMInvalidArgumentException.php b/lib/Doctrine/ORM/ORMInvalidArgumentException.php
index 81466a0fe..accf1cc15 100644
--- a/lib/Doctrine/ORM/ORMInvalidArgumentException.php
+++ b/lib/Doctrine/ORM/ORMInvalidArgumentException.php
@@ -210,6 +210,18 @@ class ORMInvalidArgumentException extends \InvalidArgumentException
         ));
     }
 
+    /**
+     * Used when a given entityName hasn't the good type
+     *
+     * @param mixed $entityName The given entity (which shouldn't be a string)
+     *
+     * @return self
+     */
+    public static function invalidEntityName($entityName)
+    {
+        return new self(sprintf('Entity name must be a string, %s given', gettype($entityName)));
+    }
+
     /**
      * Helper method to show an object as string.
      *
diff --git a/lib/Doctrine/ORM/UnitOfWork.php b/lib/Doctrine/ORM/UnitOfWork.php
index fbbab7b6a..368fdfd63 100644
--- a/lib/Doctrine/ORM/UnitOfWork.php
+++ b/lib/Doctrine/ORM/UnitOfWork.php
@@ -2360,6 +2360,8 @@ class UnitOfWork implements PropertyChangedListener
      * @param string|null $entityName if given, only entities of this type will get detached.
      *
      * @return void
+     *
+     * @throws ORMInvalidArgumentException if an invalid entity name is given
      */
     public function clear($entityName = null)
     {
diff --git a/tests/Doctrine/Tests/ORM/EntityManagerTest.php b/tests/Doctrine/Tests/ORM/EntityManagerTest.php
index d0cf2bcbb..954a3f2f0 100644
--- a/tests/Doctrine/Tests/ORM/EntityManagerTest.php
+++ b/tests/Doctrine/Tests/ORM/EntityManagerTest.php
@@ -3,15 +3,20 @@
 namespace Doctrine\Tests\ORM;
 
 use Doctrine\Common\Persistence\Mapping\Driver\MappingDriver;
+use Doctrine\Common\Persistence\Mapping\MappingException;
 use Doctrine\ORM\Configuration;
 use Doctrine\ORM\EntityManager;
 use Doctrine\ORM\ORMException;
 use Doctrine\ORM\ORMInvalidArgumentException;
 use Doctrine\ORM\Query\ResultSetMapping;
+use Doctrine\Tests\Models\GeoNames\Country;
 use Doctrine\Tests\OrmTestCase;
 
 class EntityManagerTest extends OrmTestCase
 {
+    /**
+     * @var EntityManager
+     */
     private $_em;
 
     function setUp()
@@ -69,7 +74,7 @@ class EntityManagerTest extends OrmTestCase
     }
 
     /**
-     * @covers Doctrine\ORM\EntityManager::createNamedNativeQuery
+     * @covers \Doctrine\ORM\EntityManager::createNamedNativeQuery
      */
     public function testCreateNamedNativeQuery()
     {
@@ -217,4 +222,60 @@ class EntityManagerTest extends OrmTestCase
         $config->setMetadataDriverImpl($this->createMock(MappingDriver::class));
         EntityManager::create(1, $config);
     }
+
+    /**
+     * @group 6017
+     */
+    public function testClearManagerWithObject()
+    {
+        $entity = new Country(456, 'United Kingdom');
+
+        $this->expectException(ORMInvalidArgumentException::class);
+
+        $this->_em->clear($entity);
+    }
+
+    /**
+     * @group 6017
+     */
+    public function testClearManagerWithUnknownEntityName()
+    {
+        $this->expectException(MappingException::class);
+
+        $this->_em->clear(uniqid('nonExisting', true));
+    }
+
+    /**
+     * @group 6017
+     */
+    public function testClearManagerWithProxyClassName()
+    {
+        $proxy = $this->_em->getReference(Country::class, ['id' => rand(457, 100000)]);
+
+        $entity = new Country(456, 'United Kingdom');
+
+        $this->_em->persist($entity);
+
+        $this->assertTrue($this->_em->contains($entity));
+
+        $this->_em->clear(get_class($proxy));
+
+        $this->assertFalse($this->_em->contains($entity));
+    }
+
+    /**
+     * @group 6017
+     */
+    public function testClearManagerWithNullValue()
+    {
+        $entity = new Country(456, 'United Kingdom');
+
+        $this->_em->persist($entity);
+
+        $this->assertTrue($this->_em->contains($entity));
+
+        $this->_em->clear(null);
+
+        $this->assertFalse($this->_em->contains($entity));
+    }
 }
diff --git a/tests/Doctrine/Tests/ORM/ORMInvalidArgumentExceptionTest.php b/tests/Doctrine/Tests/ORM/ORMInvalidArgumentExceptionTest.php
new file mode 100644
index 000000000..81f22e2b7
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/ORMInvalidArgumentExceptionTest.php
@@ -0,0 +1,60 @@
+<?php
+
+namespace Doctrine\Tests\ORM;
+
+use Doctrine\Common\Collections\ArrayCollection;
+use Doctrine\Common\NotifyPropertyChanged;
+use Doctrine\Common\PropertyChangedListener;
+use Doctrine\ORM\Mapping\ClassMetadata;
+use Doctrine\ORM\ORMInvalidArgumentException;
+use Doctrine\ORM\UnitOfWork;
+use Doctrine\ORM\ORMException;
+use Doctrine\Tests\Mocks\ConnectionMock;
+use Doctrine\Tests\Mocks\DriverMock;
+use Doctrine\Tests\Mocks\EntityManagerMock;
+use Doctrine\Tests\Mocks\EntityPersisterMock;
+use Doctrine\Tests\Mocks\UnitOfWorkMock;
+use Doctrine\Tests\Models\CMS\CmsPhonenumber;
+use Doctrine\Tests\Models\CMS\CmsUser;
+use Doctrine\Tests\Models\Forum\ForumAvatar;
+use Doctrine\Tests\Models\Forum\ForumUser;
+use Doctrine\Tests\Models\GeoNames\City;
+use Doctrine\Tests\Models\GeoNames\Country;
+use Doctrine\Tests\OrmTestCase;
+use stdClass;
+
+/**
+ * @covers \Doctrine\ORM\ORMInvalidArgumentException
+ */
+class ORMInvalidArgumentExceptionTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @dataProvider invalidEntityNames
+     *
+     * @param mixed  $value
+     * @param string $expectedMessage
+     *
+     * @return void
+     */
+    public function testInvalidEntityName($value, $expectedMessage)
+    {
+        $exception = ORMInvalidArgumentException::invalidEntityName($value);
+
+        self::assertInstanceOf(ORMInvalidArgumentException::class, $exception);
+        self::assertSame($expectedMessage, $exception->getMessage());
+    }
+
+    /**
+     * @return string[][]
+     */
+    public function invalidEntityNames()
+    {
+        return [
+            [null, 'Entity name must be a string, NULL given'],
+            [true, 'Entity name must be a string, boolean given'],
+            [123, 'Entity name must be a string, integer given'],
+            [123.45, 'Entity name must be a string, double given'],
+            [new \stdClass(), 'Entity name must be a string, object given'],
+        ];
+    }
+}
diff --git a/tests/Doctrine/Tests/ORM/UnitOfWorkTest.php b/tests/Doctrine/Tests/ORM/UnitOfWorkTest.php
index 0ff2572b9..5a32d2882 100644
--- a/tests/Doctrine/Tests/ORM/UnitOfWorkTest.php
+++ b/tests/Doctrine/Tests/ORM/UnitOfWorkTest.php
@@ -4,10 +4,12 @@ namespace Doctrine\Tests\ORM;
 
 use Doctrine\Common\Collections\ArrayCollection;
 use Doctrine\Common\NotifyPropertyChanged;
+use Doctrine\Common\Persistence\Mapping\MappingException;
 use Doctrine\Common\PropertyChangedListener;
 use Doctrine\ORM\Mapping\ClassMetadata;
 use Doctrine\ORM\ORMInvalidArgumentException;
 use Doctrine\ORM\UnitOfWork;
+use Doctrine\ORM\ORMException;
 use Doctrine\Tests\Mocks\ConnectionMock;
 use Doctrine\Tests\Mocks\DriverMock;
 use Doctrine\Tests\Mocks\EntityManagerMock;