diff --git a/src/Illuminate/Database/Eloquent/Relations/BelongsTo.php b/src/Illuminate/Database/Eloquent/Relations/BelongsTo.php
index 8bde76a0c388..112a0edba022 100755
--- a/src/Illuminate/Database/Eloquent/Relations/BelongsTo.php
+++ b/src/Illuminate/Database/Eloquent/Relations/BelongsTo.php
@@ -2,6 +2,7 @@
 
 namespace Illuminate\Database\Eloquent\Relations;
 
+use BackedEnum;
 use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Database\Eloquent\Collection;
 use Illuminate\Database\Eloquent\Model;
@@ -375,7 +376,9 @@ protected function getRelatedKeyFrom(Model $model)
      */
     protected function getForeignKeyFrom(Model $model)
     {
-        return $model->{$this->foreignKey};
+        $foreignKey = $model->{$this->foreignKey};
+
+        return $foreignKey instanceof BackedEnum ? $foreignKey->value : $foreignKey;
     }
 
     /**
diff --git a/src/Illuminate/Database/Query/Builder.php b/src/Illuminate/Database/Query/Builder.php
index 62abc80023c8..546624662f34 100755
--- a/src/Illuminate/Database/Query/Builder.php
+++ b/src/Illuminate/Database/Query/Builder.php
@@ -1161,7 +1161,7 @@ public function whereIntegerInRaw($column, $values, $boolean = 'and', $not = fal
         $values = Arr::flatten($values);
 
         foreach ($values as &$value) {
-            $value = (int) $value;
+            $value = (int) ($value instanceof BackedEnum ? $value->value : $value);
         }
 
         $this->wheres[] = compact('type', 'column', 'values', 'boolean');
diff --git a/tests/Database/DatabaseEloquentBelongsToTest.php b/tests/Database/DatabaseEloquentBelongsToTest.php
index 0c392e704412..1ace437a4346 100755
--- a/tests/Database/DatabaseEloquentBelongsToTest.php
+++ b/tests/Database/DatabaseEloquentBelongsToTest.php
@@ -6,6 +6,7 @@
 use Illuminate\Database\Eloquent\Collection;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Tests\Database\Fixtures\Enums\Bar;
 use Mockery as m;
 use PHPUnit\Framework\TestCase;
 
@@ -85,6 +86,16 @@ public function testIdsInEagerConstraintsCanBeZero()
         $relation->addEagerConstraints($models);
     }
 
+    public function testIdsInEagerConstraintsCanBeBackedEnum()
+    {
+        $relation = $this->getRelation();
+        $relation->getRelated()->shouldReceive('getKeyName')->andReturn('id');
+        $relation->getRelated()->shouldReceive('getKeyType')->andReturn('int');
+        $relation->getQuery()->shouldReceive('whereIntegerInRaw')->once()->with('relation.id', [5, 'foreign.value']);
+        $models = [new EloquentBelongsToModelStub, new EloquentBelongsToModelStubWithBackedEnumCast];
+        $relation->addEagerConstraints($models);
+    }
+
     public function testRelationIsProperlyInitialized()
     {
         $relation = $this->getRelation();
@@ -119,6 +130,15 @@ public function __toString()
             }
         };
 
+        $result4 = new class extends Model
+        {
+            protected $casts = [
+                'id' => Bar::class,
+            ];
+
+            protected $attributes = ['id' => 5];
+        };
+
         $model1 = new EloquentBelongsToModelStub;
         $model1->foreign_key = 1;
         $model2 = new EloquentBelongsToModelStub;
@@ -131,11 +151,18 @@ public function __toString()
                 return '3';
             }
         };
-        $models = $relation->match([$model1, $model2, $model3], new Collection([$result1, $result2, $result3]), 'foo');
+        $model4 = new EloquentBelongsToModelStub;
+        $model4->foreign_key = 5;
+        $models = $relation->match(
+            [$model1, $model2, $model3, $model4],
+            new Collection([$result1, $result2, $result3, $result4]),
+            'foo'
+        );
 
         $this->assertEquals(1, $models[0]->foo->getAttribute('id'));
         $this->assertEquals(2, $models[1]->foo->getAttribute('id'));
         $this->assertSame('3', (string) $models[2]->foo->getAttribute('id'));
+        $this->assertEquals(5, $models[3]->foo->getAttribute('id')->value);
     }
 
     public function testAssociateMethodSetsForeignKeyOnModel()
@@ -403,3 +430,14 @@ class MissingEloquentBelongsToModelStub extends Model
 {
     public $foreign_key;
 }
+
+class EloquentBelongsToModelStubWithBackedEnumCast extends Model
+{
+    protected $casts = [
+        'foreign_key' => Bar::class,
+    ];
+
+    public $attributes = [
+        'foreign_key' => 5,
+    ];
+}
diff --git a/tests/Database/DatabaseQueryBuilderTest.php b/tests/Database/DatabaseQueryBuilderTest.php
index 011e22c99afb..5be1c956db9b 100755
--- a/tests/Database/DatabaseQueryBuilderTest.php
+++ b/tests/Database/DatabaseQueryBuilderTest.php
@@ -23,6 +23,7 @@
 use Illuminate\Pagination\Cursor;
 use Illuminate\Pagination\CursorPaginator;
 use Illuminate\Pagination\LengthAwarePaginator;
+use Illuminate\Tests\Database\Fixtures\Enums\Bar;
 use InvalidArgumentException;
 use Mockery as m;
 use PHPUnit\Framework\TestCase;
@@ -1039,8 +1040,10 @@ public function testEmptyWhereNotIns()
     public function testWhereIntegerInRaw()
     {
         $builder = $this->getBuilder();
-        $builder->select('*')->from('users')->whereIntegerInRaw('id', ['1a', 2]);
-        $this->assertSame('select * from "users" where "id" in (1, 2)', $builder->toSql());
+        $builder->select('*')->from('users')->whereIntegerInRaw('id', [
+            '1a', 2, Bar::FOO,
+        ]);
+        $this->assertSame('select * from "users" where "id" in (1, 2, 5)', $builder->toSql());
         $this->assertEquals([], $builder->getBindings());
 
         $builder = $this->getBuilder();
@@ -1048,8 +1051,9 @@ public function testWhereIntegerInRaw()
             ['id' => '1a'],
             ['id' => 2],
             ['any' => '3'],
+            ['id' => Bar::FOO],
         ]);
-        $this->assertSame('select * from "users" where "id" in (1, 2, 3)', $builder->toSql());
+        $this->assertSame('select * from "users" where "id" in (1, 2, 3, 5)', $builder->toSql());
         $this->assertEquals([], $builder->getBindings());
     }
 
diff --git a/tests/Database/Fixtures/Enums/Bar.php b/tests/Database/Fixtures/Enums/Bar.php
new file mode 100644
index 000000000000..bc019a9be02c
--- /dev/null
+++ b/tests/Database/Fixtures/Enums/Bar.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Illuminate\Tests\Database\Fixtures\Enums;
+
+enum Bar: int
+{
+    case FOO = 5;
+}