diff --git a/pydanticrud/backends/dynamodb.py b/pydanticrud/backends/dynamodb.py
index 3dc8b8f..8dddaa3 100644
--- a/pydanticrud/backends/dynamodb.py
+++ b/pydanticrud/backends/dynamodb.py
@@ -123,7 +123,7 @@ def index_definition(index_name, keys, gsi=False):
 class DynamoSerializer:
     def __init__(self, schema, ttl_field=None):
         self.properties = schema.get("properties")
-        self.definitions = schema.get("definitions")
+        self.definitions = schema.get("definitions", {})
         self.ttl_field = ttl_field
 
     def _get_type_possibilities(self, field_name) -> Set[tuple]: