diff --git a/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php b/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php
index 495218e5550..29aca9be230 100644
--- a/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php
+++ b/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php
@@ -384,14 +384,6 @@ private function addInheritedFields(ClassMetadata $subClass, ClassMetadata $pare
     private function addInheritedRelations(ClassMetadata $subClass, ClassMetadata $parentClass): void
     {
         foreach ($parentClass->associationMappings as $field => $mapping) {
-            if ($parentClass->isMappedSuperclass) {
-                if ($mapping['type'] & ClassMetadata::TO_MANY && ! $mapping['isOwningSide']) {
-                    throw MappingException::illegalToManyAssociationOnMappedSuperclass($parentClass->name, $field);
-                }
-
-                $mapping['sourceEntity'] = $subClass->name;
-            }
-
             if (! isset($mapping['inherited']) && ! $parentClass->isMappedSuperclass) {
                 $mapping['inherited'] = $parentClass->name;
             }
@@ -400,6 +392,20 @@ private function addInheritedRelations(ClassMetadata $subClass, ClassMetadata $p
                 $mapping['declared'] = $parentClass->name;
             }
 
+            // When the class inheriting the relation ($subClass) is the first entity class since the
+            // relation has been defined in a mapped superclass (or in a chain
+            // of mapped superclasses) above, then declare this current entity class as the source of
+            // the relationship.
+            // According to the definitions given in https://github.com/doctrine/orm/pull/10396/,
+            // this is the case <=> ! isset($mapping['inherited']).
+            if (! isset($mapping['inherited'])) {
+                if ($mapping['type'] & ClassMetadata::TO_MANY && ! $mapping['isOwningSide']) {
+                    throw MappingException::illegalToManyAssociationOnMappedSuperclass($parentClass->name, $field);
+                }
+
+                $mapping['sourceEntity'] = $subClass->name;
+            }
+
             $subClass->addInheritedAssociationMapping($mapping);
         }
     }
diff --git a/tests/Doctrine/Tests/ORM/Functional/Ticket/GH5998Test.php b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH5998Test.php
new file mode 100644
index 00000000000..028bced80ba
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH5998Test.php
@@ -0,0 +1,255 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\ORM\Functional\Ticket;
+
+use Doctrine\DBAL\LockMode;
+use Doctrine\ORM\Mapping as ORM;
+use Doctrine\Tests\OrmFunctionalTestCase;
+
+/**
+ * @group GH-5998
+ */
+class GH5998Test extends OrmFunctionalTestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->_schemaTool->createSchema([
+            $this->_em->getClassMetadata(GH5998JTI::class),
+            $this->_em->getClassMetadata(GH5998JTIChild::class),
+            $this->_em->getClassMetadata(GH5998STI::class),
+            $this->_em->getClassMetadata(GH5998Basic::class),
+            $this->_em->getClassMetadata(GH5998Related::class),
+        ]);
+    }
+
+    /**
+     * Verifies that MappedSuperclasses work within an inheritance hierarchy.
+     */
+    public function testIssue(): void
+    {
+        // Test JTI
+        $this->classTests(GH5998JTIChild::class);
+        // Test STI
+        $this->classTests(GH5998STIChild::class);
+        // Test Basic
+        $this->classTests(GH5998Basic::class);
+    }
+
+    private function classTests($className): void
+    {
+        // Test insert
+        $child      = new $className('Sam', 0, 1);
+        $child->rel = new GH5998Related();
+        $this->_em->persist($child);
+        $this->_em->persist($child->rel);
+        $this->_em->flush();
+        $this->_em->clear();
+
+        // Test find by rel
+        $child = $this->_em->getRepository($className)->findOneBy(['rel' => $child->rel]);
+        self::assertNotNull($child);
+        $this->_em->clear();
+
+        // Test query by id with fetch join
+        $child = $this->_em->createQuery('SELECT t, r FROM ' . $className . ' t JOIN t.rel r WHERE t.id = 1')->getOneOrNullResult();
+        self::assertNotNull($child);
+
+        // Test lock and update
+        $this->_em->transactional(static function ($em) use ($child): void {
+            $em->lock($child, LockMode::NONE);
+            $child->firstName = 'Bob';
+            $child->status    = 0;
+        });
+        $this->_em->clear();
+        $child = $this->_em->getRepository($className)->find(1);
+        self::assertEquals($child->firstName, 'Bob');
+        self::assertEquals($child->status, 0);
+
+        // Test delete
+        $this->_em->remove($child);
+        $this->_em->flush();
+        $child = $this->_em->getRepository($className)->find(1);
+        self::assertNull($child);
+    }
+}
+
+/**
+ * @ORM\MappedSuperclass
+ */
+class GH5998Common
+{
+    /**
+     * @ORM\Id
+     * @ORM\Column(type="integer")
+     * @ORM\GeneratedValue
+     *
+     * @var int
+     */
+    public $id;
+    /**
+     * @ORM\ManyToOne(targetEntity=GH5998Related::class)
+     * @ORM\JoinColumn(name="related_id", referencedColumnName="id")
+     *
+     * @var GH5998Related
+     */
+    public $rel;
+    /**
+     * @ORM\Version
+     * @ORM\Column(type="integer")
+     *
+     * @var int
+     */
+    public $version;
+
+    /** @var mixed */
+    public $other;
+}
+
+/**
+ * @ORM\Entity
+ * @ORM\InheritanceType("JOINED")
+ * @ORM\DiscriminatorMap({"child" = GH5998JTIChild::class})
+ */
+abstract class GH5998JTI extends GH5998Common
+{
+    /**
+     * @ORM\Column(type="string", length=255)
+     *
+     * @var string
+     */
+    public $firstName;
+}
+
+/**
+ * @ORM\MappedSuperclass
+ */
+class GH5998JTICommon extends GH5998JTI
+{
+    /**
+     * @ORM\Column(type="integer")
+     *
+     * @var int
+     */
+    public $status;
+}
+
+/**
+ * @ORM\Entity
+ */
+class GH5998JTIChild extends GH5998JTICommon
+{
+    /**
+     * @ORM\Column(type="integer")
+     *
+     * @var int
+     */
+    public $type;
+
+    public function __construct(string $firstName, int $type, int $status)
+    {
+        $this->firstName = $firstName;
+        $this->type      = $type;
+        $this->status    = $status;
+    }
+}
+
+/**
+ * @ORM\Entity
+ * @ORM\InheritanceType("SINGLE_TABLE")
+ * @ORM\DiscriminatorMap({"child" = GH5998STIChild::class})
+ */
+abstract class GH5998STI extends GH5998Common
+{
+    /**
+     * @ORM\Column(type="string", length=255)
+     *
+     * @var string
+     */
+    public $firstName;
+}
+
+/**
+ * @ORM\MappedSuperclass
+ */
+class GH5998STICommon extends GH5998STI
+{
+    /**
+     * @ORM\Column(type="integer")
+     *
+     * @var int
+     */
+    public $status;
+}
+
+/**
+ * @ORM\Entity
+ */
+class GH5998STIChild extends GH5998STICommon
+{
+    /**
+     * @ORM\Column(type="integer")
+     *
+     * @var int
+     */
+    public $type;
+
+    public function __construct(string $firstName, int $type, int $status)
+    {
+        $this->firstName = $firstName;
+        $this->type      = $type;
+        $this->status    = $status;
+    }
+}
+
+/**
+ * @ORM\Entity
+ */
+class GH5998Basic extends GH5998Common
+{
+    /**
+     * @ORM\Column(type="string", length=255)
+     *
+     * @var string
+     */
+    public $firstName;
+
+    /**
+     * @ORM\Column(type="integer")
+     *
+     * @var int
+     */
+    public $status;
+
+    /**
+     * @ORM\Column(type="integer")
+     *
+     * @var int
+     */
+    public $type;
+
+    public function __construct(string $firstName, int $type, int $status)
+    {
+        $this->firstName = $firstName;
+        $this->type      = $type;
+        $this->status    = $status;
+    }
+}
+
+/**
+ * @ORM\Entity()
+ */
+class GH5998Related
+{
+    /**
+     * @ORM\Id
+     * @ORM\Column(type="integer")
+     * @ORM\GeneratedValue
+     *
+     * @var int
+     */
+    public $id;
+}
diff --git a/tests/Doctrine/Tests/ORM/Functional/Ticket/GH8415Test.php b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH8415Test.php
new file mode 100644
index 00000000000..9ce30802660
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH8415Test.php
@@ -0,0 +1,121 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\ORM\Functional\Ticket;
+
+use Doctrine\ORM\Mapping as ORM;
+use Doctrine\Tests\OrmFunctionalTestCase;
+
+class GH8415Test extends OrmFunctionalTestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->setUpEntitySchema(
+            [
+                GH8415BaseClass::class,
+                GH8415MiddleMappedSuperclass::class,
+                GH8415LeafClass::class,
+                GH8415AssociationTarget::class,
+            ]
+        );
+    }
+
+    public function testAssociationIsBasedOnBaseClass(): void
+    {
+        $target            = new GH8415AssociationTarget();
+        $leaf              = new GH8415LeafClass();
+        $leaf->baseField   = 'base';
+        $leaf->middleField = 'middle';
+        $leaf->leafField   = 'leaf';
+        $leaf->target      = $target;
+
+        $this->_em->persist($target);
+        $this->_em->persist($leaf);
+        $this->_em->flush();
+        $this->_em->clear();
+
+        $query  = $this->_em->createQuery('SELECT leaf FROM Doctrine\Tests\ORM\Functional\Ticket\GH8415LeafClass leaf JOIN leaf.target t');
+        $result = $query->getOneOrNullResult();
+
+        $this->assertInstanceOf(GH8415LeafClass::class, $result);
+        $this->assertSame('base', $result->baseField);
+        $this->assertSame('middle', $result->middleField);
+        $this->assertSame('leaf', $result->leafField);
+    }
+}
+
+/**
+ * @ORM\Entity
+ */
+class GH8415AssociationTarget
+{
+    /**
+     * @ORM\Column(type="integer")
+     * @ORM\Id
+     * @ORM\GeneratedValue
+     *
+     * @var int
+     */
+    public $id;
+}
+
+/**
+ * @ORM\Entity
+ * @ORM\InheritanceType("JOINED")
+ * @ORM\DiscriminatorColumn(name="discriminator", type="string")
+ * @ORM\DiscriminatorMap({"1" = "Doctrine\Tests\ORM\Functional\Ticket\GH8415BaseClass", "2" = "Doctrine\Tests\ORM\Functional\Ticket\GH8415LeafClass"})
+ */
+class GH8415BaseClass
+{
+    /**
+     * @ORM\Column(type="integer")
+     * @ORM\Id
+     * @ORM\GeneratedValue
+     *
+     * @var int
+     */
+    public $id;
+
+    /**
+     * @ORM\ManyToOne(targetEntity="GH8415AssociationTarget")
+     *
+     * @var GH8415AssociationTarget
+     */
+    public $target;
+
+    /**
+     * @ORM\Column(type="string")
+     *
+     * @var string
+     */
+    public $baseField;
+}
+
+/**
+ * @ORM\MappedSuperclass
+ */
+class GH8415MiddleMappedSuperclass extends GH8415BaseClass
+{
+    /**
+     * @ORM\Column(type="string")
+     *
+     * @var string
+     */
+    public $middleField;
+}
+
+/**
+ * @ORM\Entity
+ */
+class GH8415LeafClass extends GH8415MiddleMappedSuperclass
+{
+    /**
+     * @ORM\Column(type="string")
+     *
+     * @var string
+     */
+    public $leafField;
+}
diff --git a/tests/Doctrine/Tests/ORM/Functional/Ticket/GH8415ToManyAssociationTest.php b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH8415ToManyAssociationTest.php
new file mode 100644
index 00000000000..c5a7c35f3df
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH8415ToManyAssociationTest.php
@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\ORM\Functional\Ticket;
+
+use Doctrine\Common\Collections\Collection;
+use Doctrine\ORM\Mapping as ORM;
+use Doctrine\Tests\OrmTestCase;
+
+class GH8415ToManyAssociationTest extends OrmTestCase
+{
+    public function testToManyAssociationOnBaseClassAllowedWhenThereAreMappedSuperclassesAsChildren(): void
+    {
+        $this->expectNotToPerformAssertions();
+
+        $em = $this->getTestEntityManager();
+        $em->getClassMetadata(GH8415ToManyLeafClass::class);
+    }
+}
+
+/**
+ * @ORM\Entity
+ */
+class GH8415ToManyAssociationTarget
+{
+    /**
+     * @ORM\Column(type="integer")
+     * @ORM\Id
+     * @ORM\GeneratedValue
+     *
+     * @var int
+     */
+    public $id;
+
+    /**
+     * @ORM\ManyToOne(targetEntity="GH8415ToManyBaseClass", inversedBy="targets")
+     *
+     * @var GH8415ToManyBaseClass
+     */
+    public $base;
+}
+
+/**
+ * @ORM\Entity
+ * @ORM\InheritanceType("SINGLE_TABLE")
+ * @ORM\DiscriminatorColumn(name="discriminator", type="string")
+ * @ORM\DiscriminatorMap({"1" = "Doctrine\Tests\ORM\Functional\Ticket\GH8415ToManyBaseClass", "2" = "Doctrine\Tests\ORM\Functional\Ticket\GH8415ToManyLeafClass"})
+ */
+class GH8415ToManyBaseClass
+{
+    /**
+     * @ORM\Column(type="integer")
+     * @ORM\Id
+     * @ORM\GeneratedValue
+     *
+     * @var int
+     */
+    public $id;
+
+    /**
+     * @ORM\OneToMany(targetEntity="GH8415ToManyAssociationTarget", mappedBy="base")
+     *
+     * @var Collection
+     */
+    public $targets;
+}
+
+/**
+ * @ORM\MappedSuperclass
+ */
+class GH8415ToManyMappedSuperclass extends GH8415ToManyBaseClass
+{
+}
+
+/**
+ * @ORM\Entity
+ */
+class GH8415ToManyLeafClass extends GH8415ToManyMappedSuperclass
+{
+    /**
+     * @ORM\Column(type="string")
+     *
+     * @var string
+     */
+    public $leafField;
+}