diff --git a/modules/core/resources/META-INF/smithy/openapi/openapi.smithy b/modules/core/resources/META-INF/smithy/openapi/openapi.smithy
index 1c47d4d..10ca384 100644
--- a/modules/core/resources/META-INF/smithy/openapi/openapi.smithy
+++ b/modules/core/resources/META-INF/smithy/openapi/openapi.smithy
@@ -5,6 +5,7 @@ namespace alloy.openapi
 /// This traits allows the encoding of OpenAPI Extensions
 /// as defined in https://swagger.io/docs/specification/openapi-extensions/.
 @trait
+@sparse
 map openapiExtensions {
     key: String
     value: Document