diff --git a/ts/smartdata.classes.collection.ts b/ts/smartdata.classes.collection.ts
index 00ddd80..e9b1bb7 100644
--- a/ts/smartdata.classes.collection.ts
+++ b/ts/smartdata.classes.collection.ts
@@ -45,8 +45,8 @@ export interface IManager {
   db: SmartdataDb
 }
 
-export const setDefaultManagerForDoc = (managerArg: IManager,  dbDocArg: any) => {
-  dbDocArg.prototype.defaultManager = managerArg;
+export const setDefaultManagerForDoc = <T>(managerArg: IManager,  dbDocArg: T): T => {
+  (dbDocArg as any).prototype.defaultManager = managerArg;
   return dbDocArg;
 }