diff --git a/tests/Doctrine/Tests/ORM/Functional/Ticket/GH6776Test.php b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH6776Test.php
new file mode 100644
index 00000000000..9406bd06042
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH6776Test.php
@@ -0,0 +1,125 @@
+<?php
+
+namespace Doctrine\Tests\ORM\Functional\Ticket;
+
+use Doctrine\Common\Collections\ArrayCollection;
+use Doctrine\Tests\OrmFunctionalTestCase;
+
+/**
+ * @group GH-6776
+ */
+class GH6776Test extends OrmFunctionalTestCase
+{
+    /**
+     * {@inheritDoc}
+     */
+    protected function setUp() : void
+    {
+        parent::setUp();
+
+        $this->_schemaTool->createSchema([
+            $this->_em->getClassMetadata(GH6776WheelDimension::class),
+            $this->_em->getClassMetadata(GH6776Vehicle::class),
+        ]);
+    }
+
+    /**
+     * Verifies that removing and then inserting an element in a collection using a unique constraint does not
+     * make this constraint fail.
+     */
+    public function testIssue() : void
+    {
+        // create some vehicle with dimensions
+        $vehicle                    = new GH6776Vehicle();
+        $vehicle->name              = 'SuperCar';
+
+        $dimension1                 = new GH6776WheelDimension();
+        $dimension1->width          = 6;
+        $dimension1->diameter       = 17;
+        $dimension1->offset         = 32;
+        $dimension1->tirePressure   = 2.75;
+        $dimension1->vehicle        = $vehicle;
+
+        $dimension1bis              = clone $dimension1;
+
+        $dimension2                 = new GH6776WheelDimension();
+        $dimension2->type           = 'rear';
+        $dimension2->width          = 6;
+        $dimension2->diameter       = 17;
+        $dimension2->offset         = 39;
+        $dimension2->tirePressure   = 2.75;
+        $dimension2->vehicle        = $vehicle;
+
+        $vehicle->compatibleDimensions = new ArrayCollection();
+        $vehicle->compatibleDimensions->add($dimension1);
+        $vehicle->compatibleDimensions->add($dimension2);
+
+        // persist and flush vehicle and the 2 original dimensions
+        $this->_em->persist($vehicle);
+        $this->_em->persist($dimension1);
+        $this->_em->persist($dimension2);
+
+        $this->_em->flush();
+
+        $this->assertCount(2, $vehicle->compatibleDimensions);
+
+        // remove dimension1 and add its clone; when flushing it should crash because of unique constraint violation
+        $vehicle->compatibleDimensions->removeElement($dimension1);
+        $this->_em->remove($dimension1);
+
+        $this->assertCount(1, $vehicle->compatibleDimensions);
+
+        $this->_em->persist($dimension1bis);
+        $vehicle->compatibleDimensions->add($dimension1bis);
+
+        $this->_em->flush();
+
+        // still the same count
+        $this->assertCount(2, $vehicle->compatibleDimensions);
+    }
+}
+
+/**
+ * Class GH6776Vehicle
+ * @Entity
+ */
+class GH6776Vehicle
+{
+    /** @Id @Column(type="integer") @GeneratedValue */
+    public $id;
+
+    /** @Column(type="string") */
+    public $name;
+
+    /** @oneToMany(targetEntity="GH6776WheelDimension", mappedBy="vehicle") */
+    public $compatibleDimensions;
+}
+
+/**
+ * Class GH6776WheelDimension
+ * @Entity
+ * @Table(uniqueConstraints={@UniqueConstraint(name="wheel_size", columns={"offset", "width", "diameter"})})
+ */
+class GH6776WheelDimension
+{
+    /** @Id @Column(type="integer") @GeneratedValue */
+    public $id;
+
+    /** @ManyToOne(targetEntity="GH6776Vehicle", inversedBy="compatibleDimensions") */
+    public $vehicle;
+
+    /** @Column(type="integer") */
+    public $offset;
+
+    /** @Column(type="integer") */
+    public $width;
+
+    /** @Column(type="integer") */
+    public $diameter;
+
+    /** @Column(type="float") */
+    public $tirePressure;
+
+    /** @Column(type="string") */
+    public $type = 'front';
+}