diff --git a/synapse/api/auth/base.py b/synapse/api/auth/base.py
index c63607a6a6..e78ad7b21b 100644
--- a/synapse/api/auth/base.py
+++ b/synapse/api/auth/base.py
@@ -314,7 +314,8 @@ class BaseAuth:
             client_address, IPv6Address
         ):
             logger.error(
-                "Unable to view IP address of the requester. Check that you are setting the X-Forwarded-For header correctly in your reverse proxy. Assuming '127.0.0.1'"
+                "Unable to view IP address of the requester. " \
+                "Check that you are setting the X-Forwarded-For header correctly in your reverse proxy."
             )
             raise SynapseError(
                 HTTPStatus.INTERNAL_SERVER_ERROR,
diff --git a/tests/api/test_auth.py b/tests/api/test_auth.py
index e7fcd928d7..1907a33112 100644
--- a/tests/api/test_auth.py
+++ b/tests/api/test_auth.py
@@ -23,6 +23,7 @@ from unittest.mock import AsyncMock, Mock
 
 import pymacaroons
 
+from twisted.internet.address import IPv4Address
 from twisted.internet.testing import MemoryReactor
 
 from synapse.api.auth.internal import InternalAuth
@@ -118,7 +119,7 @@ class AuthTestCase(unittest.HomeserverTestCase):
         self.store.get_user_by_access_token = AsyncMock(return_value=None)
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
         requester = self.get_success(self.auth.get_user_by_req(request))
@@ -137,7 +138,7 @@ class AuthTestCase(unittest.HomeserverTestCase):
         self.store.get_user_by_access_token = AsyncMock(return_value=None)
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "192.168.10.10"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="192.168.10.10", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
         requester = self.get_success(self.auth.get_user_by_req(request))
@@ -156,7 +157,7 @@ class AuthTestCase(unittest.HomeserverTestCase):
         self.store.get_user_by_access_token = AsyncMock(return_value=None)
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "131.111.8.42"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="131.111.8.42", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
         f = self.get_failure(
@@ -209,7 +210,7 @@ class AuthTestCase(unittest.HomeserverTestCase):
         self.store.get_user_by_access_token = AsyncMock(return_value=None)
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.args[b"user_id"] = [masquerading_user_id]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
@@ -231,7 +232,7 @@ class AuthTestCase(unittest.HomeserverTestCase):
         self.store.get_user_by_access_token = AsyncMock(return_value=None)
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.args[b"user_id"] = [masquerading_user_id]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
@@ -261,7 +262,7 @@ class AuthTestCase(unittest.HomeserverTestCase):
         self.store.get_device = AsyncMock(return_value={"hidden": False})
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.args[b"user_id"] = [masquerading_user_id]
         request.args[b"org.matrix.msc3202.device_id"] = [masquerading_device_id]
@@ -296,7 +297,7 @@ class AuthTestCase(unittest.HomeserverTestCase):
         self.store.get_device = AsyncMock(return_value=None)
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.args[b"user_id"] = [masquerading_user_id]
         request.args[b"org.matrix.msc3202.device_id"] = [masquerading_device_id]
@@ -320,7 +321,7 @@ class AuthTestCase(unittest.HomeserverTestCase):
         self.store.mark_access_token_as_used = AsyncMock(return_value=None)
         self.store.get_user_locked_status = AsyncMock(return_value=False)
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
         self.get_success(self.auth.get_user_by_req(request))
@@ -341,7 +342,7 @@ class AuthTestCase(unittest.HomeserverTestCase):
         self.store.insert_client_ip = AsyncMock(return_value=None)
         self.store.mark_access_token_as_used = AsyncMock(return_value=None)
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
         self.get_success(self.auth.get_user_by_req(request))
diff --git a/tests/handlers/test_cas.py b/tests/handlers/test_cas.py
index f677f3be2a..1135b38f2f 100644
--- a/tests/handlers/test_cas.py
+++ b/tests/handlers/test_cas.py
@@ -21,6 +21,7 @@
 from typing import Any, Dict
 from unittest.mock import AsyncMock, Mock
 
+from twisted.internet.address import IPv4Address
 from twisted.internet.testing import MemoryReactor
 
 from synapse.handlers.cas import CasResponse
@@ -234,6 +235,7 @@ def _mock_request() -> Mock:
             "write",
         ]
     )
+    mock.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
     # `_disconnected` musn't be another `Mock`, otherwise it will be truthy.
     mock._disconnected = False
     return mock
diff --git a/tests/handlers/test_oidc.py b/tests/handlers/test_oidc.py
index 5207382f00..37a006fa0f 100644
--- a/tests/handlers/test_oidc.py
+++ b/tests/handlers/test_oidc.py
@@ -25,6 +25,7 @@ from urllib.parse import parse_qs, urlparse
 
 import pymacaroons
 
+from twisted.internet.address import IPv4Address
 from twisted.internet.testing import MemoryReactor
 
 from synapse.handlers.sso import MappingException
@@ -1684,5 +1685,5 @@ def _build_callback_request(
     request.args = {}
     request.args[b"code"] = [code.encode("utf-8")]
     request.args[b"state"] = [state.encode("utf-8")]
-    request.getClientAddress.return_value.host = ip_address
+    request.getClientAddress.return_value = IPv4Address(type="TCP", host=ip_address, port=12345)
     return request
diff --git a/tests/handlers/test_saml.py b/tests/handlers/test_saml.py
index f7cbf91113..77c07564d9 100644
--- a/tests/handlers/test_saml.py
+++ b/tests/handlers/test_saml.py
@@ -24,6 +24,7 @@ from unittest.mock import AsyncMock, Mock
 
 import attr
 
+from twisted.internet.address import IPv4Address
 from twisted.internet.testing import MemoryReactor
 
 from synapse.api.errors import RedirectException
@@ -424,4 +425,5 @@ def _mock_request() -> Mock:
     )
     # `_disconnected` musn't be another `Mock`, otherwise it will be truthy.
     mock._disconnected = False
+    mock.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
     return mock