diff --git a/src/flask_session/__init__.py b/src/flask_session/__init__.py
index 738ab75a..9798d55f 100644
--- a/src/flask_session/__init__.py
+++ b/src/flask_session/__init__.py
@@ -3,7 +3,6 @@
     FileSystemSessionInterface,
     MemcachedSessionInterface,
     MongoDBSessionInterface,
-    NullSessionInterface,
     RedisSessionInterface,
     SqlAlchemySessionInterface,
 )
@@ -150,6 +149,6 @@ def _get_interface(self, app):
                 bind_key=SESSION_SQLALCHEMY_BIND_KEY,
             )
         else:
-            session_interface = NullSessionInterface()
+            raise RuntimeError(f"Unrecognized value for SESSION_TYPE: {SESSION_TYPE}")
 
         return session_interface
diff --git a/src/flask_session/sessions.py b/src/flask_session/sessions.py
index f34d82a0..bd41af14 100644
--- a/src/flask_session/sessions.py
+++ b/src/flask_session/sessions.py
@@ -79,18 +79,6 @@ def _sign(self, app, sid):
         return signer.sign(sid_as_bytes).decode("utf-8")
 
 
-class NullSessionInterface(SessionInterface):
-    """Used to open a :class:`flask.sessions.NullSession` instance.
-
-    If you do not configure a different ``SESSION_TYPE``, this will be used to
-    generate nicer error messages.  Will allow read-only access to the empty
-    session but fail on setting.
-    """
-
-    def open_session(self, app, request):
-        return None
-
-
 class ServerSideSessionInterface(SessionInterface, ABC):
     """Used to open a :class:`flask.sessions.ServerSideSessionInterface` instance."""