diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 541cda8..568254e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -13,7 +13,7 @@ jobs:
         strategy:
             fail-fast: false
             matrix:
-                php: ['7.2.5', '7.3', '7.4', '8.0']
+                php: ['7.2.5', '7.3', '7.4', '8.0', '8.1']
                 include:
                     - php: '7.4'
                       deps: lowest
diff --git a/Tests/Domain/AuditLoggerTest.php b/Tests/Domain/AuditLoggerTest.php
index 05e9c82..afe886d 100644
--- a/Tests/Domain/AuditLoggerTest.php
+++ b/Tests/Domain/AuditLoggerTest.php
@@ -11,7 +11,11 @@
 
 namespace Symfony\Component\Security\Acl\Tests\Domain;
 
-class AuditLoggerTest extends \PHPUnit\Framework\TestCase
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Security\Acl\Domain\AuditLogger;
+use Symfony\Component\Security\Acl\Tests\Fixtures\SerializableAuditableEntryInterface;
+
+class AuditLoggerTest extends TestCase
 {
     /**
      * @dataProvider getTestLogData
@@ -73,11 +77,11 @@ public function getTestLogData()
 
     protected function getEntry()
     {
-        return $this->createMock('Symfony\Component\Security\Acl\Model\AuditableEntryInterface');
+        return $this->createMock(SerializableAuditableEntryInterface::class);
     }
 
     protected function getLogger()
     {
-        return $this->getMockForAbstractClass('Symfony\Component\Security\Acl\Domain\AuditLogger');
+        return $this->getMockForAbstractClass(AuditLogger::class);
     }
 }
diff --git a/Tests/Domain/EntryTest.php b/Tests/Domain/EntryTest.php
index 116269e..a69e3b9 100644
--- a/Tests/Domain/EntryTest.php
+++ b/Tests/Domain/EntryTest.php
@@ -11,9 +11,12 @@
 
 namespace Symfony\Component\Security\Acl\Tests\Domain;
 
+use PHPUnit\Framework\TestCase;
 use Symfony\Component\Security\Acl\Domain\Entry;
+use Symfony\Component\Security\Acl\Model\SecurityIdentityInterface;
+use Symfony\Component\Security\Acl\Tests\Fixtures\SerializableAclInterface;
 
-class EntryTest extends \PHPUnit\Framework\TestCase
+class EntryTest extends TestCase
 {
     public function testConstructor()
     {
@@ -77,7 +80,7 @@ public function testSerializeUnserialize()
         $uAce = unserialize($serialized);
 
         $this->assertNull($uAce->getAcl());
-        $this->assertInstanceOf('Symfony\Component\Security\Acl\Model\SecurityIdentityInterface', $uAce->getSecurityIdentity());
+        $this->assertInstanceOf(SecurityIdentityInterface::class, $uAce->getSecurityIdentity());
         $this->assertEquals($ace->getId(), $uAce->getId());
         $this->assertEquals($ace->getMask(), $uAce->getMask());
         $this->assertEquals($ace->getStrategy(), $uAce->getStrategy());
@@ -109,11 +112,11 @@ protected function getAce($acl = null, $sid = null)
 
     protected function getAcl()
     {
-        return $this->createMock('Symfony\Component\Security\Acl\Model\AclInterface');
+        return $this->createMock(SerializableAclInterface::class);
     }
 
     protected function getSid()
     {
-        return $this->createMock('Symfony\Component\Security\Acl\Model\SecurityIdentityInterface');
+        return $this->createMock(SecurityIdentityInterface::class);
     }
 }
diff --git a/Tests/Domain/FieldEntryTest.php b/Tests/Domain/FieldEntryTest.php
index b7452cc..7b29fd8 100644
--- a/Tests/Domain/FieldEntryTest.php
+++ b/Tests/Domain/FieldEntryTest.php
@@ -11,10 +11,12 @@
 
 namespace Symfony\Component\Security\Acl\Tests\Domain;
 
+use PHPUnit\Framework\TestCase;
 use Symfony\Component\Security\Acl\Domain\FieldEntry;
 use Symfony\Component\Security\Acl\Model\SecurityIdentityInterface;
+use Symfony\Component\Security\Acl\Tests\Fixtures\SerializableAclInterface;
 
-class FieldEntryTest extends \PHPUnit\Framework\TestCase
+class FieldEntryTest extends TestCase
 {
     public function testConstructor()
     {
@@ -31,7 +33,7 @@ public function testSerializeUnserialize()
         $uAce = unserialize($serialized);
 
         $this->assertNull($uAce->getAcl());
-        $this->assertInstanceOf('Symfony\Component\Security\Acl\Model\SecurityIdentityInterface', $uAce->getSecurityIdentity());
+        $this->assertInstanceOf(SecurityIdentityInterface::class, $uAce->getSecurityIdentity());
         $this->assertEquals($ace->getId(), $uAce->getId());
         $this->assertEquals($ace->getField(), $uAce->getField());
         $this->assertEquals($ace->getMask(), $uAce->getMask());
@@ -86,11 +88,11 @@ protected function getAce($acl = null, $sid = null)
 
     protected function getAcl()
     {
-        return $this->createMock('Symfony\Component\Security\Acl\Model\AclInterface');
+        return $this->createMock(SerializableAclInterface::class);
     }
 
     protected function getSid()
     {
-        return $this->createMock('Symfony\Component\Security\Acl\Model\SecurityIdentityInterface');
+        return $this->createMock(SecurityIdentityInterface::class);
     }
 }
diff --git a/Tests/Fixtures/SerializableAclInterface.php b/Tests/Fixtures/SerializableAclInterface.php
new file mode 100644
index 0000000..94e8230
--- /dev/null
+++ b/Tests/Fixtures/SerializableAclInterface.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace Symfony\Component\Security\Acl\Tests\Fixtures;
+
+use Symfony\Component\Security\Acl\Model\AclInterface;
+
+interface SerializableAclInterface extends AclInterface
+{
+    public function __serialize(): array;
+
+    public function __unserialize(array $data): void;
+}
diff --git a/Tests/Fixtures/SerializableAuditableEntryInterface.php b/Tests/Fixtures/SerializableAuditableEntryInterface.php
new file mode 100644
index 0000000..b88e271
--- /dev/null
+++ b/Tests/Fixtures/SerializableAuditableEntryInterface.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace Symfony\Component\Security\Acl\Tests\Fixtures;
+
+use Symfony\Component\Security\Acl\Model\AuditableEntryInterface;
+
+interface SerializableAuditableEntryInterface extends AuditableEntryInterface
+{
+    public function __serialize(): array;
+
+    public function __unserialize(array $data): void;
+}
diff --git a/Tests/Voter/AclVoterTest.php b/Tests/Voter/AclVoterTest.php
index f1830c7..a596810 100644
--- a/Tests/Voter/AclVoterTest.php
+++ b/Tests/Voter/AclVoterTest.php
@@ -17,11 +17,11 @@
 use Symfony\Component\Security\Acl\Domain\UserSecurityIdentity;
 use Symfony\Component\Security\Acl\Exception\AclNotFoundException;
 use Symfony\Component\Security\Acl\Exception\NoAceFoundException;
-use Symfony\Component\Security\Acl\Model\AclInterface;
 use Symfony\Component\Security\Acl\Model\AclProviderInterface;
 use Symfony\Component\Security\Acl\Model\ObjectIdentityRetrievalStrategyInterface;
 use Symfony\Component\Security\Acl\Model\SecurityIdentityRetrievalStrategyInterface;
 use Symfony\Component\Security\Acl\Permission\PermissionMapInterface;
+use Symfony\Component\Security\Acl\Tests\Fixtures\SerializableAclInterface;
 use Symfony\Component\Security\Acl\Voter\AclVoter;
 use Symfony\Component\Security\Acl\Voter\FieldVote;
 use Symfony\Component\Security\Core\Authentication\Token\TokenInterface;
@@ -220,7 +220,7 @@ public function testVoteGrantsAccess($grant)
             ->expects($this->once())
             ->method('findAcl')
             ->with($this->equalTo($oid), $this->equalTo($sids))
-            ->willReturn($acl = $this->createMock(AclInterface::class))
+            ->willReturn($acl = $this->createMock(SerializableAclInterface::class))
         ;
 
         $acl
@@ -266,7 +266,7 @@ public function testVoteNoAceFound()
             ->expects($this->once())
             ->method('findAcl')
             ->with($this->equalTo($oid), $this->equalTo($sids))
-            ->willReturn($acl = $this->createMock(AclInterface::class))
+            ->willReturn($acl = $this->createMock(SerializableAclInterface::class))
         ;
 
         $acl
@@ -309,7 +309,7 @@ public function testVoteGrantsFieldAccess($grant)
             ->expects($this->once())
             ->method('findAcl')
             ->with($this->equalTo($oid), $this->equalTo($sids))
-            ->willReturn($acl = $this->createMock(AclInterface::class))
+            ->willReturn($acl = $this->createMock(SerializableAclInterface::class))
         ;
 
         $acl
@@ -355,7 +355,7 @@ public function testVoteNoFieldAceFound()
             ->expects($this->once())
             ->method('findAcl')
             ->with($this->equalTo($oid), $this->equalTo($sids))
-            ->willReturn($acl = $this->createMock(AclInterface::class))
+            ->willReturn($acl = $this->createMock(SerializableAclInterface::class))
         ;
 
         $acl
@@ -396,7 +396,7 @@ public function testWhenReceivingAnObjectIdentityInterfaceWeDontRetrieveANewObje
             ->expects($this->once())
             ->method('findAcl')
             ->with($this->equalTo($oid), $this->equalTo($sids))
-            ->willReturn($acl = $this->createMock(AclInterface::class))
+            ->willReturn($acl = $this->createMock(SerializableAclInterface::class))
         ;
 
         $acl