diff --git a/CHANGES/3207.bugfix b/CHANGES/3207.bugfix
new file mode 100644
index 00000000000..4966019d307
--- /dev/null
+++ b/CHANGES/3207.bugfix
@@ -0,0 +1,2 @@
+Accept ``CIMultiDictProxy`` instances for ``headers`` argument in ``web.Response``
+constructor.
diff --git a/aiohttp/web_response.py b/aiohttp/web_response.py
index f3fc59e43d6..73c71fd3285 100644
--- a/aiohttp/web_response.py
+++ b/aiohttp/web_response.py
@@ -458,7 +458,7 @@ def __init__(self, *,
 
         if headers is None:
             headers = CIMultiDict()
-        elif not isinstance(headers, (CIMultiDict, CIMultiDictProxy)):
+        elif not isinstance(headers, CIMultiDict):
             headers = CIMultiDict(headers)
         else:
             headers = cast(CIMultiDict, headers)
diff --git a/tests/test_web_response.py b/tests/test_web_response.py
index 8e970fe1a66..94b0e410295 100644
--- a/tests/test_web_response.py
+++ b/tests/test_web_response.py
@@ -5,7 +5,7 @@
 from unittest import mock
 
 import pytest
-from multidict import CIMultiDict
+from multidict import CIMultiDict, CIMultiDictProxy
 
 from aiohttp import HttpVersion, HttpVersion10, HttpVersion11, hdrs, signals
 from aiohttp.payload import BytesPayload
@@ -1105,6 +1105,13 @@ def test_response_with_content_length_header_without_body() -> None:
     assert resp.content_length == 123
 
 
+def test_response_with_immutable_headers() -> None:
+    resp = Response(text='text',
+                    headers=CIMultiDictProxy(CIMultiDict({'Header': 'Value'})))
+    assert resp.headers == {'Header': 'Value',
+                            'Content-Type': 'text/plain; charset=utf-8'}
+
+
 class TestJSONResponse:
 
     def test_content_type_is_application_json_by_default(self) -> None: