diff --git a/flask_marshmallow/__init__.py b/flask_marshmallow/__init__.py
index 24a7edd..f24c834 100755
--- a/flask_marshmallow/__init__.py
+++ b/flask_marshmallow/__init__.py
@@ -124,5 +124,5 @@ def init_app(self, app):
         # If using Flask-SQLAlchemy, attach db.session to ModelSchema
         if has_sqla and 'sqlalchemy' in app.extensions:
             db = app.extensions['sqlalchemy'].db
-            self.ModelSchema.OPTIONS_CLASS.session = db.session
+            self.ModelSchema.session = db.session
         app.extensions[EXTENSION_NAME] = self