diff --git a/CONTRIBUTING.rst b/CONTRIBUTING.rst
index 8793b138..1e670329 100644
--- a/CONTRIBUTING.rst
+++ b/CONTRIBUTING.rst
@@ -8,7 +8,7 @@ Navigate to the project directory and run the following commands:
 Create and activate a virtual environment
 
 .. code-block:: bash
-    
+
     $ python -m venv .venv
     $ source .venv/bin/activate
 
@@ -16,7 +16,7 @@ Install dependencies
 
 .. code-block:: bash
 
-    $ pip install -r requirements/dev.in
+    $ pip install -r requirements/dev.txt
     $ pip install -r requirements/docs.in
 
 Install the package in editable mode
@@ -47,11 +47,11 @@ or
 Run the tests together or individually
 
 .. code-block:: bash
-    
+
     $ pytest tests
     $ pytest tests/test_basic.py
 
-For easier startup and teardown of storage for testing you may use 
+For easier startup and teardown of storage for testing you may use
 
 .. code-block:: bash
 
@@ -62,13 +62,13 @@ Using rye
 ~~~~~~~~~~~
 
 .. code-block:: bash
-    
+
     $ rye pin 3.11
     $ rye sync
 
 
 .. code-block:: bash
-    
+
     $ rye run python examples/hello.py
 
 
@@ -78,4 +78,4 @@ Pull requests
 --------------
 Please check previous pull requests before submitting a new one.
 
-Please ensure your pull requests are to the `development` branch.
\ No newline at end of file
+Please ensure your pull requests are to the `development` branch.
diff --git a/src/flask_session/__init__.py b/src/flask_session/__init__.py
index b95a0b05..5dae02aa 100644
--- a/src/flask_session/__init__.py
+++ b/src/flask_session/__init__.py
@@ -21,13 +21,13 @@ class Session:
         your Flask applications. You should always use :class:`flask.session`.
     """
 
-    def __init__(self, app=None):
+    def __init__(self, app=None, custom_interface=None):
         self.app = app
         if app is not None:
-            self.init_app(app)
+            self.init_app(app, custom_interface)
 
-    def init_app(self, app):
-        """This the the alternate setup method, typically used in an application factory pattern::
+    def init_app(self, app, custom_interface=None):
+        """This the alternate setup method, typically used in an application factory pattern::
 
             sess = Session()
 
@@ -37,8 +37,9 @@ def create_app():
                 return app
 
         :param app: the Flask app object with proper configuration.
+        :param custom_interface: a custom session interface to use.
         """
-        app.session_interface = self._get_interface(app)
+        app.session_interface = custom_interface or self._get_interface(app)
 
     def _get_interface(self, app):
         config = app.config
diff --git a/tests/test_basic.py b/tests/test_basic.py
index 1a904266..43b15bb8 100644
--- a/tests/test_basic.py
+++ b/tests/test_basic.py
@@ -2,6 +2,8 @@
 import flask_session
 import pytest
 
+from flask_session.mongodb import MongoDBSessionInterface
+
 
 def test_null_session():
     """Invalid session should fail to get/set the flask session"""
@@ -9,3 +11,16 @@ def test_null_session():
         app = flask.Flask(__name__)
         app.secret_key = "alsdkfjaldkjsf"
         flask_session.Session(app)
+
+
+class CustomInterface(MongoDBSessionInterface):
+    def hello(self):
+        return "world"
+
+
+def test_init_app_with_custom_interface():
+    """Test init_app with a custom session interface"""
+    app = flask.Flask(__name__)
+    flask_session.Session(app, custom_interface=CustomInterface(app=app))
+    assert isinstance(app.session_interface, CustomInterface)
+    assert app.session_interface.hello() == "world"