diff --git a/tests/ModelTest.php b/tests/ModelTest.php
index 21523c7..1042a07 100644
--- a/tests/ModelTest.php
+++ b/tests/ModelTest.php
@@ -16,10 +16,14 @@
 use Jenssegers\Mongodb\Eloquent\Model;
 use Jenssegers\Mongodb\Tests\Models\Book;
 use Jenssegers\Mongodb\Tests\Models\Guarded;
+use Jenssegers\Mongodb\Tests\Models\IdIsBinaryUuid;
+use Jenssegers\Mongodb\Tests\Models\IdIsInt;
+use Jenssegers\Mongodb\Tests\Models\IdIsString;
 use Jenssegers\Mongodb\Tests\Models\Item;
 use Jenssegers\Mongodb\Tests\Models\MemberStatus;
 use Jenssegers\Mongodb\Tests\Models\Soft;
 use Jenssegers\Mongodb\Tests\Models\User;
+use MongoDB\BSON\Binary;
 use MongoDB\BSON\ObjectID;
 use MongoDB\BSON\UTCDateTime;
 
@@ -325,11 +329,103 @@ public function testSoftDelete(): void
         $this->assertEquals(2, Soft::count());
     }
 
-    public function testPrimaryKey(): void
+    /**
+     * @dataProvider provideId
+     */
+    public function testPrimaryKey(string $model, $id, $expected, bool $expectedFound): void
+    {
+        $model::truncate();
+        $expectedType = get_debug_type($expected);
+
+        $document = new $model;
+        $this->assertEquals('_id', $document->getKeyName());
+
+        $document->_id = $id;
+        $document->save();
+        $this->assertSame($expectedType, get_debug_type($document->_id));
+        $this->assertEquals($expected, $document->_id);
+        $this->assertSame($expectedType, get_debug_type($document->getKey()));
+        $this->assertEquals($expected, $document->getKey());
+
+        $check = $model::find($id);
+
+        if ($expectedFound) {
+            $this->assertNotNull($check, 'Not found');
+            $this->assertSame($expectedType, get_debug_type($check->_id));
+            $this->assertEquals($id, $check->_id);
+            $this->assertSame($expectedType, get_debug_type($check->getKey()));
+            $this->assertEquals($id, $check->getKey());
+        } else {
+            $this->assertNull($check, 'Found');
+        }
+    }
+
+    public static function provideId(): iterable
+    {
+        yield 'int' => [
+            'model' => User::class,
+            'id' => 10,
+            'expected' => 10,
+            // Don't expect this to be found, as the int is cast to string for the query
+            'expectedFound' => false,
+        ];
+
+        yield 'cast as int' => [
+            'model' => IdIsInt::class,
+            'id' => 10,
+            'expected' => 10,
+            'expectedFound' => true,
+        ];
+
+        yield 'string' => [
+            'model' => User::class,
+            'id' => 'user-10',
+            'expected' => 'user-10',
+            'expectedFound' => true,
+        ];
+
+        yield 'cast as string' => [
+            'model' => IdIsString::class,
+            'id' => 'user-10',
+            'expected' => 'user-10',
+            'expectedFound' => true,
+        ];
+
+        $objectId = new ObjectID();
+        yield 'ObjectID' => [
+            'model' => User::class,
+            'id' => $objectId,
+            'expected' => (string) $objectId,
+            'expectedFound' => true,
+        ];
+
+        $binaryUuid = new Binary(hex2bin('0c103357380648c9a84b867dcb625cfb'), Binary::TYPE_UUID);
+        yield 'BinaryUuid' => [
+            'model' => User::class,
+            'id' => $binaryUuid,
+            'expected' => (string) $binaryUuid,
+            'expectedFound' => true,
+        ];
+
+        yield 'cast as BinaryUuid' => [
+            'model' => IdIsBinaryUuid::class,
+            'id' => $binaryUuid,
+            'expected' => (string) $binaryUuid,
+            'expectedFound' => true,
+        ];
+
+        $date = new UTCDateTime();
+        yield 'UTCDateTime' => [
+            'model' => User::class,
+            'id' => $date,
+            'expected' => $date,
+            // Don't expect this to be found, as the original value is stored as UTCDateTime but then cast to string
+            'expectedFound' => false,
+        ];
+    }
+
+    public function testCustomPrimaryKey(): void
     {
-        $user = new User;
-        $this->assertEquals('_id', $user->getKeyName());
-
         $book = new Book;
         $this->assertEquals('title', $book->getKeyName());
 
diff --git a/tests/Models/IdIsBinaryUuid.php b/tests/Models/IdIsBinaryUuid.php
new file mode 100644
index 0000000..1d8c592
--- /dev/null
+++ b/tests/Models/IdIsBinaryUuid.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Jenssegers\Mongodb\Tests\Models;
+
+use Jenssegers\Mongodb\Eloquent\Casts\BinaryUuid;
+use Jenssegers\Mongodb\Eloquent\Model as Eloquent;
+
+class IdIsBinaryUuid extends Eloquent
+{
+    protected $connection = 'mongodb';
+    protected static $unguarded = true;
+    protected $casts = [
+        '_id' => BinaryUuid::class,
+    ];
+}
diff --git a/tests/Models/IdIsInt.php b/tests/Models/IdIsInt.php
new file mode 100644
index 0000000..d721320
--- /dev/null
+++ b/tests/Models/IdIsInt.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Jenssegers\Mongodb\Tests\Models;
+
+use Jenssegers\Mongodb\Eloquent\Model as Eloquent;
+
+class IdIsInt extends Eloquent
+{
+    protected $keyType = 'int';
+    protected $connection = 'mongodb';
+    protected static $unguarded = true;
+    protected $casts = [
+        '_id' => 'int',
+    ];
+}
diff --git a/tests/Models/IdIsString.php b/tests/Models/IdIsString.php
new file mode 100644
index 0000000..48a2845
--- /dev/null
+++ b/tests/Models/IdIsString.php
@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Jenssegers\Mongodb\Tests\Models;
+
+use Jenssegers\Mongodb\Eloquent\Model as Eloquent;
+
+class IdIsString extends Eloquent
+{
+    protected $connection = 'mongodb';
+    protected static $unguarded = true;
+    protected $casts = [
+        '_id' => 'string',
+    ];
+}