diff --git a/index.d.ts b/index.d.ts
index 66d0e06b2..e781520c3 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -507,7 +507,7 @@ export interface IExtensionMapField extends IMapField {
 }
 
 /** Abstract runtime message. */
-export class Message<T extends object> {
+export class Message<T extends object = object> {
 
     /**
      * Constructs a new message instance.