diff --git a/scrapy/responsetypes.py b/scrapy/responsetypes.py
index 180cb094e..46dc28efb 100644
--- a/scrapy/responsetypes.py
+++ b/scrapy/responsetypes.py
@@ -11,7 +11,19 @@ from scrapy.utils.python import binary_is_text, to_bytes, to_unicode
 from scrapy.utils.response import _MIME_TYPES
 
 
-class ResponseTypes:
+class _ResponseTypesMeta(type):
+
+    def __getattribute__(self, name):
+        if name == 'CLASSES':
+            warn(
+                'scrapy.responsetypes.ResponseTypes.CLASSES is deprecated',
+                ScrapyDeprecationWarning,
+                stacklevel=2,
+            )
+        return type.__getattribute__(self, name)
+
+
+class ResponseTypes(metaclass=_ResponseTypesMeta):
 
     CLASSES = {
         'text/html': 'scrapy.http.HtmlResponse',
@@ -47,6 +59,15 @@ class ResponseTypes:
         for mimetype, cls in self.CLASSES.items():
             self.classes[mimetype] = load_object(cls)
 
+    def __getattribute__(self, name):
+        if name == 'CLASSES':
+            warn(
+                'scrapy.responsetypes.ResponseTypes.CLASSES is deprecated',
+                ScrapyDeprecationWarning,
+                stacklevel=2,
+            )
+        return super().__getattribute__(name)
+
     def from_mimetype(self, mimetype):
         """Return the most appropriate Response class for the given mimetype"""
         warn('ResponseTypes.from_mimetype is deprecated, '
diff --git a/tests/test_responsetypes.py b/tests/test_responsetypes.py
index 4ce41f086..434993c0b 100644
--- a/tests/test_responsetypes.py
+++ b/tests/test_responsetypes.py
@@ -127,6 +127,24 @@ class ResponseTypesTest(unittest.TestCase):
         messages = {str(warning.message) for warning in warnings}
         self.assertIn(expected_message, messages)
 
+    def test_class_classes_deprecation(self):
+        with catch_warnings(record=True) as warnings:
+            ResponseTypes.CLASSES
+        expected_message = (
+            'scrapy.responsetypes.ResponseTypes.CLASSES is deprecated'
+        )
+        messages = {str(warning.message) for warning in warnings}
+        self.assertIn(expected_message, messages)
+
+    def test_instance_classes_deprecation(self):
+        with catch_warnings(record=True) as warnings:
+            responsetypes.CLASSES
+        expected_message = (
+            'scrapy.responsetypes.ResponseTypes.CLASSES is deprecated'
+        )
+        messages = {str(warning.message) for warning in warnings}
+        self.assertIn(expected_message, messages)
+
 
 if __name__ == "__main__":
     unittest.main()