diff --git a/src/Namespace.d.ts b/src/Namespace.d.ts
index 9749679..e1be201 100644
--- a/src/Namespace.d.ts
+++ b/src/Namespace.d.ts
@@ -134,6 +134,7 @@ interface ApiContract {
   expects: string;
   examples: string;
   supportedOperation: string;
+  messageId: string;
   statusCode: string;
   method: string;
   required: string;
@@ -257,7 +258,7 @@ interface Vocabularies {
   core: Readonly<Core>;
   security: Readonly<Security>;
   apiContract: Readonly<ApiContract>;
-  apiBinding: Readonly<ApiBinding>
+  apiBinding: Readonly<ApiBinding>;
   shapes: Readonly<Shapes>;
   data: Readonly<Data>;
   docSourceMaps: Readonly<DocSourceMaps>;
diff --git a/src/Namespace.js b/src/Namespace.js
index 5c76470..4bf8d2b 100644
--- a/src/Namespace.js
+++ b/src/Namespace.js
@@ -155,6 +155,7 @@ ns.aml.vocabularies.apiContract.response = `${contractKey}response`;
 ns.aml.vocabularies.apiContract.returns = `${contractKey}returns`;
 ns.aml.vocabularies.apiContract.expects = `${contractKey}expects`;
 ns.aml.vocabularies.apiContract.examples = `${contractKey}examples`;
+ns.aml.vocabularies.apiContract.messageId = `${contractKey}messageId`;
 ns.aml.vocabularies.apiContract.supportedOperation = `${contractKey}supportedOperation`;
 ns.aml.vocabularies.apiContract.statusCode = `${contractKey}statusCode`;
 ns.aml.vocabularies.apiContract.method = `${contractKey}method`;