diff --git a/cacholote/config.py b/cacholote/config.py
index 978ddf3..2274fdf 100644
--- a/cacholote/config.py
+++ b/cacholote/config.py
@@ -88,23 +88,20 @@ def make_cache_dir(self) -> "Settings":
         fs.mkdirs(urlpath, exist_ok=True)
         return self
 
-    @pydantic.model_validator(mode="after")
-    def check_mutually_exclusive(self) -> "Settings":
-        mutually_exclusive = (self.sessionmaker, self.cache_db_urlpath)
-        if all(mutually_exclusive) or not any(mutually_exclusive):
-            raise ValueError(
-                "Provide either `sessionmaker` or `cache_db_urlpath` (mutually exclusive)."
-            )
-        return self
-
     @property
     def instantiated_sessionmaker(self) -> sa.orm.sessionmaker:  # type: ignore[type-arg]
         if self.sessionmaker is None:
+            if self.cache_db_urlpath is None:
+                raise ValueError("Provide either `sessionmaker` or `cache_db_urlpath`.")
             self.sessionmaker = database.cached_sessionmaker(
                 self.cache_db_urlpath, **self.create_engine_kwargs
             )
             self.cache_db_urlpath = None
             self.create_engine_kwargs = {}
+        elif self.cache_db_urlpath is not None:
+            raise ValueError(
+                "`sessionmaker` and `cache_db_urlpath` are mutually exclusive."
+            )
         return self.sessionmaker
 
     @property
diff --git a/cacholote/database.py b/cacholote/database.py
index 3c1ae6e..52b5128 100644
--- a/cacholote/database.py
+++ b/cacholote/database.py
@@ -18,7 +18,7 @@
 import functools
 import json
 import warnings
-from typing import Any
+from typing import Any, Dict
 
 import sqlalchemy as sa
 import sqlalchemy.orm
@@ -77,8 +77,32 @@ def _commit_or_rollback(session: sa.orm.Session) -> None:
         session.rollback()
 
 
+def _encode_kwargs(**kwargs: Any) -> Dict[str, Any]:
+    encoded_kwargs = {}
+    for key, value in kwargs.items():
+        if isinstance(value, dict):
+            encoded_kwargs["_encoded_" + key] = json.dumps(value)
+        else:
+            encoded_kwargs[key] = value
+    return encoded_kwargs
+
+
+def _decode_kwargs(**kwargs: Any) -> Dict[str, Any]:
+    decoded_kwargs = {}
+    for key, value in kwargs.items():
+        if key.startswith("_encoded_"):
+            decoded_kwargs[key.replace("_encoded_", "", 1)] = json.loads(value)
+        else:
+            decoded_kwargs[key] = value
+    return decoded_kwargs
+
+
 @functools.lru_cache()
-def cached_sessionmaker(url: str, **kwargs: Any) -> sa.orm.sessionmaker:  # type: ignore[type-arg]
-    engine = sa.create_engine(url, **kwargs)
+def _cached_sessionmaker(url: str, **kwargs: Any) -> sa.orm.sessionmaker:  # type: ignore[type-arg]
+    engine = sa.create_engine(url, **_decode_kwargs(**kwargs))
     Base.metadata.create_all(engine)
     return sa.orm.sessionmaker(engine)
+
+
+def cached_sessionmaker(url: str, **kwargs: Any) -> sa.orm.sessionmaker:  # type: ignore[type-arg]
+    return _cached_sessionmaker(url, **_encode_kwargs(**kwargs))
diff --git a/tests/conftest.py b/tests/conftest.py
index 0e913c0..1d31f38 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -44,7 +44,7 @@ def set_cache(
 ) -> Iterator[str]:
     param = getattr(request, "param", "file")
     if param.lower() == "cads":
-        database.cached_sessionmaker.cache_clear()
+        database._cached_sessionmaker.cache_clear()
         test_bucket_name = "test-bucket"
         client_kwargs = create_test_bucket(s3_server, test_bucket_name)
         with config.set(
diff --git a/tests/test_01_settings.py b/tests/test_01_settings.py
index f7f42e8..1066b1f 100644
--- a/tests/test_01_settings.py
+++ b/tests/test_01_settings.py
@@ -137,3 +137,9 @@ def test_set_expiration(
 ) -> None:
     with raises:
         config.set(expiration=expiration)
+
+
+def test_create_engine_dict_kwargs() -> None:
+    old_session_maker = config.get().instantiated_sessionmaker
+    config.set(create_engine_kwargs={"connect_args": {"timeout": 30}})
+    assert config.get().instantiated_sessionmaker is not old_session_maker