diff --git a/scrapy/spiders/__init__.py b/scrapy/spiders/__init__.py
index c08bb964a..4b2771415 100644
--- a/scrapy/spiders/__init__.py
+++ b/scrapy/spiders/__init__.py
@@ -75,9 +75,8 @@ class Spider(object_ref):
     def parse(self, response):
         raise NotImplementedError
 
-    @classmethod
-    def update_settings(cls, settings):
-        settings.setdict(cls.custom_settings or {}, priority='spider')
+    def update_settings(self, settings):
+        settings.setdict(self.custom_settings or {}, priority='spider')
 
     @classmethod
     def handles_request(cls, request):
diff --git a/tests/test_spider.py b/tests/test_spider.py
index 4d5d4b07e..63a3d2e61 100644
--- a/tests/test_spider.py
+++ b/tests/test_spider.py
@@ -98,11 +98,17 @@ class SpiderTest(unittest.TestCase):
         self.spider_class.custom_settings = spider_settings
         settings = Settings(project_settings, priority='project')
 
-        self.spider_class.update_settings(settings)
+        spider = self.spider_class('example.com')
+        spider.update_settings(settings)
         self.assertEqual(settings.get('TEST1'), 'spider')
         self.assertEqual(settings.get('TEST2'), 'spider')
         self.assertEqual(settings.get('TEST3'), 'project')
 
+        spider_instance_settings = {'TEST1': 'spider_instance'}
+        spider.custom_settings = spider_instance_settings
+        spider.update_settings(settings)
+        self.assertEqual(settings.get('TEST1'), 'spider_instance')
+
     def test_logger(self):
         spider = self.spider_class('example.com')
         with LogCapture() as l: