diff --git a/CHANGES/3532.bugfix b/CHANGES/3532.bugfix
new file mode 100644
index 00000000000..6ee7b3b3d18
--- /dev/null
+++ b/CHANGES/3532.bugfix
@@ -0,0 +1,2 @@
+Raise a ClientResponseError instead of an AssertionError for a blank
+HTTP Reason Phrase.
\ No newline at end of file
diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index 1188ca1ccf1..5b7d89b81d5 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -120,6 +120,7 @@ Joel Watts
 Jon Nabozny
 Joongi Kim
 Josep Cugat
+Joshu Coats
 Julia Tsemusheva
 Julien Duponchelle
 Jungkook Park
diff --git a/aiohttp/client_reqrep.py b/aiohttp/client_reqrep.py
index 846ce6f090c..8785605c708 100644
--- a/aiohttp/client_reqrep.py
+++ b/aiohttp/client_reqrep.py
@@ -932,7 +932,8 @@ def release(self) -> Any:
 
     def raise_for_status(self) -> None:
         if 400 <= self.status:
-            assert self.reason  # always not None for started response
+            # reason should always be not None for a started response
+            assert self.reason is not None
             self.release()
             raise ClientResponseError(
                 self.request_info,
diff --git a/tests/test_client_response.py b/tests/test_client_response.py
index cf203d844b2..f29f9e4d084 100644
--- a/tests/test_client_response.py
+++ b/tests/test_client_response.py
@@ -669,6 +669,24 @@ def test_raise_for_status_4xx() -> None:
     assert response.closed
 
 
+def test_raise_for_status_4xx_without_reason() -> None:
+    response = ClientResponse('get', URL('http://def-cl-resp.org'),
+                              request_info=mock.Mock(),
+                              writer=mock.Mock(),
+                              continue100=None,
+                              timer=TimerNoop(),
+                              traces=[],
+                              loop=mock.Mock(),
+                              session=mock.Mock())
+    response.status = 404
+    response.reason = ''
+    with pytest.raises(aiohttp.ClientResponseError) as cm:
+        response.raise_for_status()
+    assert str(cm.value.status) == '404'
+    assert str(cm.value.message) == ''
+    assert response.closed
+
+
 def test_resp_host() -> None:
     response = ClientResponse('get', URL('http://del-cl-resp.org'),
                               request_info=mock.Mock(),