diff --git a/src/Illuminate/Database/Eloquent/Builder.php b/src/Illuminate/Database/Eloquent/Builder.php
index f3fdf50027f1..e30ecb882810 100755
--- a/src/Illuminate/Database/Eloquent/Builder.php
+++ b/src/Illuminate/Database/Eloquent/Builder.php
@@ -465,7 +465,7 @@ public function firstOrNew(array $attributes = [], array $values = [])
             return $instance;
         }
 
-        return $this->newModelInstance($attributes + $values);
+        return $this->newModelInstance(array_merge($attributes, $values));
     }
 
     /**
@@ -481,7 +481,7 @@ public function firstOrCreate(array $attributes = [], array $values = [])
             return $instance;
         }
 
-        return tap($this->newModelInstance($attributes + $values), function ($instance) {
+        return tap($this->newModelInstance(array_merge($attributes, $values)), function ($instance) {
             $instance->save();
         });
     }
diff --git a/src/Illuminate/Database/Eloquent/Relations/HasOneOrMany.php b/src/Illuminate/Database/Eloquent/Relations/HasOneOrMany.php
index f3a50501fdd6..1c7ff591cd9c 100755
--- a/src/Illuminate/Database/Eloquent/Relations/HasOneOrMany.php
+++ b/src/Illuminate/Database/Eloquent/Relations/HasOneOrMany.php
@@ -214,7 +214,7 @@ public function findOrNew($id, $columns = ['*'])
     public function firstOrNew(array $attributes = [], array $values = [])
     {
         if (is_null($instance = $this->where($attributes)->first())) {
-            $instance = $this->related->newInstance($attributes + $values);
+            $instance = $this->related->newInstance(array_merge($attributes, $values));
 
             $this->setForeignAttributesForCreate($instance);
         }
@@ -232,7 +232,7 @@ public function firstOrNew(array $attributes = [], array $values = [])
     public function firstOrCreate(array $attributes = [], array $values = [])
     {
         if (is_null($instance = $this->where($attributes)->first())) {
-            $instance = $this->create($attributes + $values);
+            $instance = $this->create(array_merge($attributes, $values));
         }
 
         return $instance;
diff --git a/tests/Database/DatabaseEloquentIntegrationTest.php b/tests/Database/DatabaseEloquentIntegrationTest.php
index 9624af06add4..f46d5e55b74c 100644
--- a/tests/Database/DatabaseEloquentIntegrationTest.php
+++ b/tests/Database/DatabaseEloquentIntegrationTest.php
@@ -401,6 +401,16 @@ public function testCursorPaginatedModelCollectionRetrievalWhenNoElementsAndDefa
         $this->assertInstanceOf(CursorPaginator::class, $models);
     }
 
+    public function testFirstOrNew()
+    {
+        $user1 = EloquentTestUser::firstOrNew(
+            ['name' => 'Dries Vints'],
+            ['name' => 'Nuno Maduro']
+        );
+
+        $this->assertSame('Nuno Maduro', $user1->name);
+    }
+
     public function testFirstOrCreate()
     {
         $user1 = EloquentTestUser::firstOrCreate(['email' => 'taylorotwell@gmail.com']);
@@ -425,6 +435,13 @@ public function testFirstOrCreate()
         $this->assertNotEquals($user3->id, $user1->id);
         $this->assertSame('abigailotwell@gmail.com', $user3->email);
         $this->assertSame('Abigail Otwell', $user3->name);
+
+        $user4 = EloquentTestUser::firstOrCreate(
+            ['name' => 'Dries Vints'],
+            ['name' => 'Nuno Maduro', 'email' => 'nuno@laravel.com']
+        );
+
+        $this->assertSame('Nuno Maduro', $user4->name);
     }
 
     public function testUpdateOrCreate()
@@ -678,6 +695,36 @@ public function testBasicModelHydration()
         $this->assertCount(1, $models);
     }
 
+    public function testFirstOrNewOnHasOneRelationShip()
+    {
+        $user1 = EloquentTestUser::create(['email' => 'taylorotwell@gmail.com']);
+        $post1 = $user1->post()->firstOrNew(['name' => 'First Post'], ['name' => 'New Post']);
+
+        $this->assertSame('New Post', $post1->name);
+
+        $user2 = EloquentTestUser::create(['email' => 'abigailotwell@gmail.com']);
+        $post = $user2->post()->create(['name' => 'First Post']);
+        $post2 = $user2->post()->firstOrNew(['name' => 'First Post'], ['name' => 'New Post']);
+
+        $this->assertSame('First Post', $post2->name);
+        $this->assertSame($post->id, $post2->id);
+    }
+
+    public function testFirstOrCreateOnHasOneRelationShip()
+    {
+        $user1 = EloquentTestUser::create(['email' => 'taylorotwell@gmail.com']);
+        $post1 = $user1->post()->firstOrCreate(['name' => 'First Post'], ['name' => 'New Post']);
+
+        $this->assertSame('New Post', $post1->name);
+
+        $user2 = EloquentTestUser::create(['email' => 'abigailotwell@gmail.com']);
+        $post = $user2->post()->create(['name' => 'First Post']);
+        $post2 = $user2->post()->firstOrCreate(['name' => 'First Post'], ['name' => 'New Post']);
+
+        $this->assertSame('First Post', $post2->name);
+        $this->assertSame($post->id, $post2->id);
+    }
+
     public function testHasOnSelfReferencingBelongsToManyRelationship()
     {
         $user = EloquentTestUser::create(['email' => 'taylorotwell@gmail.com']);