diff --git a/changelog.d/17667.misc b/changelog.d/17667.misc
new file mode 100644
index 000000000..6526f283b
--- /dev/null
+++ b/changelog.d/17667.misc
@@ -0,0 +1,5 @@
+Import pydantic objects from the `_pydantic_compat` module.
+
+This allows `check_pydantic_models.py` to mock those pydantic objects
+only in the synapse module, and not interfere with pydantic objects in
+external dependencies.
diff --git a/scripts-dev/check_pydantic_models.py b/scripts-dev/check_pydantic_models.py
index 26d667aba..5eb1f0a9d 100755
--- a/scripts-dev/check_pydantic_models.py
+++ b/scripts-dev/check_pydantic_models.py
@@ -45,7 +45,6 @@ import traceback
 import unittest.mock
 from contextlib import contextmanager
 from typing import (
-    TYPE_CHECKING,
     Any,
     Callable,
     Dict,
@@ -57,30 +56,17 @@ from typing import (
 )
 
 from parameterized import parameterized
-
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import (
-        BaseModel as PydanticBaseModel,
-        conbytes,
-        confloat,
-        conint,
-        constr,
-    )
-    from pydantic.v1.typing import get_args
-else:
-    from pydantic import (
-        BaseModel as PydanticBaseModel,
-        conbytes,
-        confloat,
-        conint,
-        constr,
-    )
-    from pydantic.typing import get_args
-
 from typing_extensions import ParamSpec
 
+from synapse._pydantic_compat import (
+    BaseModel as PydanticBaseModel,
+    conbytes,
+    confloat,
+    conint,
+    constr,
+    get_args,
+)
+
 logger = logging.getLogger(__name__)
 
 CONSTRAINED_TYPE_FACTORIES_WITH_STRICT_FLAG: List[Callable] = [
@@ -183,22 +169,16 @@ def monkeypatch_pydantic() -> Generator[None, None, None]:
         # Most Synapse code ought to import the patched objects directly from
         # `pydantic`. But we also patch their containing modules `pydantic.main` and
         # `pydantic.types` for completeness.
-        patch_basemodel1 = unittest.mock.patch(
-            "pydantic.BaseModel", new=PatchedBaseModel
+        patch_basemodel = unittest.mock.patch(
+            "synapse._pydantic_compat.BaseModel", new=PatchedBaseModel
         )
-        patch_basemodel2 = unittest.mock.patch(
-            "pydantic.main.BaseModel", new=PatchedBaseModel
-        )
-        patches.enter_context(patch_basemodel1)
-        patches.enter_context(patch_basemodel2)
+        patches.enter_context(patch_basemodel)
         for factory in CONSTRAINED_TYPE_FACTORIES_WITH_STRICT_FLAG:
             wrapper: Callable = make_wrapper(factory)
-            patch1 = unittest.mock.patch(f"pydantic.{factory.__name__}", new=wrapper)
-            patch2 = unittest.mock.patch(
-                f"pydantic.types.{factory.__name__}", new=wrapper
+            patch = unittest.mock.patch(
+                f"synapse._pydantic_compat.{factory.__name__}", new=wrapper
             )
-            patches.enter_context(patch1)
-            patches.enter_context(patch2)
+            patches.enter_context(patch)
         yield
 
 
diff --git a/synapse/_pydantic_compat.py b/synapse/_pydantic_compat.py
index a6ceeb04d..f0eedf5c6 100644
--- a/synapse/_pydantic_compat.py
+++ b/synapse/_pydantic_compat.py
@@ -19,6 +19,8 @@
 #
 #
 
+from typing import TYPE_CHECKING
+
 from packaging.version import Version
 
 try:
@@ -30,4 +32,64 @@ except ImportError:
 
 HAS_PYDANTIC_V2: bool = Version(pydantic_version).major == 2
 
-__all__ = ("HAS_PYDANTIC_V2",)
+if TYPE_CHECKING or HAS_PYDANTIC_V2:
+    from pydantic.v1 import (
+        BaseModel,
+        Extra,
+        Field,
+        MissingError,
+        PydanticValueError,
+        StrictBool,
+        StrictInt,
+        StrictStr,
+        ValidationError,
+        conbytes,
+        confloat,
+        conint,
+        constr,
+        parse_obj_as,
+        validator,
+    )
+    from pydantic.v1.error_wrappers import ErrorWrapper
+    from pydantic.v1.typing import get_args
+else:
+    from pydantic import (
+        BaseModel,
+        Extra,
+        Field,
+        MissingError,
+        PydanticValueError,
+        StrictBool,
+        StrictInt,
+        StrictStr,
+        ValidationError,
+        conbytes,
+        confloat,
+        conint,
+        constr,
+        parse_obj_as,
+        validator,
+    )
+    from pydantic.error_wrappers import ErrorWrapper
+    from pydantic.typing import get_args
+
+__all__ = (
+    "HAS_PYDANTIC_V2",
+    "BaseModel",
+    "constr",
+    "conbytes",
+    "conint",
+    "confloat",
+    "ErrorWrapper",
+    "Extra",
+    "Field",
+    "get_args",
+    "MissingError",
+    "parse_obj_as",
+    "PydanticValueError",
+    "StrictBool",
+    "StrictInt",
+    "StrictStr",
+    "ValidationError",
+    "validator",
+)
diff --git a/synapse/config/_util.py b/synapse/config/_util.py
index 32b906a1e..731b60a84 100644
--- a/synapse/config/_util.py
+++ b/synapse/config/_util.py
@@ -18,17 +18,11 @@
 # [This file includes modifications made by New Vector Limited]
 #
 #
-from typing import TYPE_CHECKING, Any, Dict, Type, TypeVar
+from typing import Any, Dict, Type, TypeVar
 
 import jsonschema
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import BaseModel, ValidationError, parse_obj_as
-else:
-    from pydantic import BaseModel, ValidationError, parse_obj_as
-
+from synapse._pydantic_compat import BaseModel, ValidationError, parse_obj_as
 from synapse.config._base import ConfigError
 from synapse.types import JsonDict, StrSequence
 
diff --git a/synapse/config/workers.py b/synapse/config/workers.py
index b013ffa35..ab896be30 100644
--- a/synapse/config/workers.py
+++ b/synapse/config/workers.py
@@ -22,17 +22,17 @@
 
 import argparse
 import logging
-from typing import TYPE_CHECKING, Any, Dict, List, Optional, Union
+from typing import Any, Dict, List, Optional, Union
 
 import attr
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import BaseModel, Extra, StrictBool, StrictInt, StrictStr
-else:
-    from pydantic import BaseModel, Extra, StrictBool, StrictInt, StrictStr
-
+from synapse._pydantic_compat import (
+    BaseModel,
+    Extra,
+    StrictBool,
+    StrictInt,
+    StrictStr,
+)
 from synapse.config._base import (
     Config,
     ConfigError,
diff --git a/synapse/events/validator.py b/synapse/events/validator.py
index 73b63b77f..8aa8d7e01 100644
--- a/synapse/events/validator.py
+++ b/synapse/events/validator.py
@@ -19,17 +19,11 @@
 #
 #
 import collections.abc
-from typing import TYPE_CHECKING, List, Type, Union, cast
+from typing import List, Type, Union, cast
 
 import jsonschema
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import Field, StrictBool, StrictStr
-else:
-    from pydantic import Field, StrictBool, StrictStr
-
+from synapse._pydantic_compat import Field, StrictBool, StrictStr
 from synapse.api.constants import (
     MAX_ALIAS_LENGTH,
     EventContentFields,
diff --git a/synapse/http/servlet.py b/synapse/http/servlet.py
index 08b8ff7af..0330f1c87 100644
--- a/synapse/http/servlet.py
+++ b/synapse/http/servlet.py
@@ -37,19 +37,17 @@ from typing import (
     overload,
 )
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import BaseModel, MissingError, PydanticValueError, ValidationError
-    from pydantic.v1.error_wrappers import ErrorWrapper
-else:
-    from pydantic import BaseModel, MissingError, PydanticValueError, ValidationError
-    from pydantic.error_wrappers import ErrorWrapper
-
 from typing_extensions import Literal
 
 from twisted.web.server import Request
 
+from synapse._pydantic_compat import (
+    BaseModel,
+    ErrorWrapper,
+    MissingError,
+    PydanticValueError,
+    ValidationError,
+)
 from synapse.api.errors import Codes, SynapseError
 from synapse.http import redact_uri
 from synapse.http.server import HttpServer
diff --git a/synapse/rest/admin/users.py b/synapse/rest/admin/users.py
index ad515bd5a..076994b87 100644
--- a/synapse/rest/admin/users.py
+++ b/synapse/rest/admin/users.py
@@ -27,7 +27,7 @@ from typing import TYPE_CHECKING, Dict, List, Optional, Tuple, Union
 
 import attr
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
+from synapse._pydantic_compat import StrictBool
 from synapse.api.constants import Direction, UserTypes
 from synapse.api.errors import Codes, NotFoundError, SynapseError
 from synapse.http.servlet import (
@@ -56,11 +56,6 @@ from synapse.types.rest import RequestBodyModel
 if TYPE_CHECKING:
     from synapse.server import HomeServer
 
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import StrictBool
-else:
-    from pydantic import StrictBool
-
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/rest/client/account.py b/synapse/rest/client/account.py
index 8daa449f9..32fa7b4ec 100644
--- a/synapse/rest/client/account.py
+++ b/synapse/rest/client/account.py
@@ -24,18 +24,12 @@ import random
 from typing import TYPE_CHECKING, List, Optional, Tuple
 from urllib.parse import urlparse
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import StrictBool, StrictStr, constr
-else:
-    from pydantic import StrictBool, StrictStr, constr
-
 import attr
 from typing_extensions import Literal
 
 from twisted.web.server import Request
 
+from synapse._pydantic_compat import StrictBool, StrictStr, constr
 from synapse.api.constants import LoginType
 from synapse.api.errors import (
     Codes,
diff --git a/synapse/rest/client/devices.py b/synapse/rest/client/devices.py
index 8313d687b..6a45a5d13 100644
--- a/synapse/rest/client/devices.py
+++ b/synapse/rest/client/devices.py
@@ -24,13 +24,7 @@ import logging
 from http import HTTPStatus
 from typing import TYPE_CHECKING, List, Optional, Tuple
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import Extra, StrictStr
-else:
-    from pydantic import Extra, StrictStr
-
+from synapse._pydantic_compat import Extra, StrictStr
 from synapse.api import errors
 from synapse.api.errors import NotFoundError, SynapseError, UnrecognizedRequestError
 from synapse.handlers.device import DeviceHandler
diff --git a/synapse/rest/client/directory.py b/synapse/rest/client/directory.py
index 11fdd0f7c..98ba5c4c2 100644
--- a/synapse/rest/client/directory.py
+++ b/synapse/rest/client/directory.py
@@ -22,17 +22,11 @@
 import logging
 from typing import TYPE_CHECKING, List, Optional, Tuple
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import StrictStr
-else:
-    from pydantic import StrictStr
-
 from typing_extensions import Literal
 
 from twisted.web.server import Request
 
+from synapse._pydantic_compat import StrictStr
 from synapse.api.errors import AuthError, Codes, NotFoundError, SynapseError
 from synapse.http.server import HttpServer
 from synapse.http.servlet import (
diff --git a/synapse/rest/client/reporting.py b/synapse/rest/client/reporting.py
index 4eee53e5a..97bd5d8c0 100644
--- a/synapse/rest/client/reporting.py
+++ b/synapse/rest/client/reporting.py
@@ -23,7 +23,7 @@ import logging
 from http import HTTPStatus
 from typing import TYPE_CHECKING, Tuple
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
+from synapse._pydantic_compat import StrictStr
 from synapse.api.errors import AuthError, Codes, NotFoundError, SynapseError
 from synapse.http.server import HttpServer
 from synapse.http.servlet import (
@@ -40,10 +40,6 @@ from ._base import client_patterns
 if TYPE_CHECKING:
     from synapse.server import HomeServer
 
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import StrictStr
-else:
-    from pydantic import StrictStr
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/rest/key/v2/remote_key_resource.py b/synapse/rest/key/v2/remote_key_resource.py
index 3c2028a2a..fea0b9706 100644
--- a/synapse/rest/key/v2/remote_key_resource.py
+++ b/synapse/rest/key/v2/remote_key_resource.py
@@ -23,17 +23,11 @@ import logging
 import re
 from typing import TYPE_CHECKING, Dict, Mapping, Optional, Set, Tuple
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import Extra, StrictInt, StrictStr
-else:
-    from pydantic import Extra, StrictInt, StrictStr
-
 from signedjson.sign import sign_json
 
 from twisted.web.server import Request
 
+from synapse._pydantic_compat import Extra, StrictInt, StrictStr
 from synapse.crypto.keyring import ServerKeyFetcher
 from synapse.http.server import HttpServer
 from synapse.http.servlet import (
diff --git a/synapse/storage/background_updates.py b/synapse/storage/background_updates.py
index efe423803..1194b58ff 100644
--- a/synapse/storage/background_updates.py
+++ b/synapse/storage/background_updates.py
@@ -40,7 +40,7 @@ from typing import (
 
 import attr
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
+from synapse._pydantic_compat import BaseModel
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.storage.engines import PostgresEngine
 from synapse.storage.types import Connection, Cursor
@@ -49,11 +49,6 @@ from synapse.util import Clock, json_encoder
 
 from . import engines
 
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import BaseModel
-else:
-    from pydantic import BaseModel
-
 if TYPE_CHECKING:
     from synapse.server import HomeServer
     from synapse.storage.database import (
diff --git a/synapse/types/handlers/sliding_sync.py b/synapse/types/handlers/sliding_sync.py
index e1b2af7a0..48badeacd 100644
--- a/synapse/types/handlers/sliding_sync.py
+++ b/synapse/types/handlers/sliding_sync.py
@@ -37,23 +37,20 @@ from typing import (
 
 import attr
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
+from synapse._pydantic_compat import Extra
 from synapse.api.constants import EventTypes
-from synapse.types import MultiWriterStreamToken, RoomStreamToken, StrCollection, UserID
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import Extra
-else:
-    from pydantic import Extra
-
 from synapse.events import EventBase
 from synapse.types import (
     DeviceListUpdates,
     JsonDict,
     JsonMapping,
+    MultiWriterStreamToken,
     Requester,
+    RoomStreamToken,
     SlidingSyncStreamToken,
+    StrCollection,
     StreamToken,
+    UserID,
 )
 from synapse.types.rest.client import SlidingSyncBody
 
diff --git a/synapse/types/rest/__init__.py b/synapse/types/rest/__init__.py
index 2b6f5ed35..183831e79 100644
--- a/synapse/types/rest/__init__.py
+++ b/synapse/types/rest/__init__.py
@@ -18,14 +18,7 @@
 # [This file includes modifications made by New Vector Limited]
 #
 #
-from typing import TYPE_CHECKING
-
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import BaseModel, Extra
-else:
-    from pydantic import BaseModel, Extra
+from synapse._pydantic_compat import BaseModel, Extra
 
 
 class RequestBodyModel(BaseModel):
diff --git a/synapse/types/rest/client/__init__.py b/synapse/types/rest/client/__init__.py
index 9f6fb087c..c739bd16b 100644
--- a/synapse/types/rest/client/__init__.py
+++ b/synapse/types/rest/client/__init__.py
@@ -20,29 +20,15 @@
 #
 from typing import TYPE_CHECKING, Dict, List, Optional, Tuple, Union
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import (
-        Extra,
-        StrictBool,
-        StrictInt,
-        StrictStr,
-        conint,
-        constr,
-        validator,
-    )
-else:
-    from pydantic import (
-        Extra,
-        StrictBool,
-        StrictInt,
-        StrictStr,
-        conint,
-        constr,
-        validator,
-    )
-
+from synapse._pydantic_compat import (
+    Extra,
+    StrictBool,
+    StrictInt,
+    StrictStr,
+    conint,
+    constr,
+    validator,
+)
 from synapse.types.rest import RequestBodyModel
 from synapse.util.threepids import validate_email
 
@@ -384,7 +370,7 @@ class SlidingSyncBody(RequestBodyModel):
         receipts: Optional[ReceiptsExtension] = None
         typing: Optional[TypingExtension] = None
 
-    conn_id: Optional[str]
+    conn_id: Optional[StrictStr]
 
     # mypy workaround via https://github.com/pydantic/pydantic/issues/156#issuecomment-1130883884
     if TYPE_CHECKING:
diff --git a/tests/rest/client/test_models.py b/tests/rest/client/test_models.py
index f8a56c80c..f14585cca 100644
--- a/tests/rest/client/test_models.py
+++ b/tests/rest/client/test_models.py
@@ -19,18 +19,12 @@
 #
 #
 import unittest as stdlib_unittest
-from typing import TYPE_CHECKING
 
 from typing_extensions import Literal
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
+from synapse._pydantic_compat import BaseModel, ValidationError
 from synapse.types.rest.client import EmailRequestTokenBody
 
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import BaseModel, ValidationError
-else:
-    from pydantic import BaseModel, ValidationError
-
 
 class ThreepidMediumEnumTestCase(stdlib_unittest.TestCase):
     class Model(BaseModel):