diff --git a/mongoose/mongoose.d.ts b/mongoose/mongoose.d.ts
index 3cd48c5ec2..8c60b638fc 100644
--- a/mongoose/mongoose.d.ts
+++ b/mongoose/mongoose.d.ts
@@ -12,7 +12,7 @@ declare module "mongoose" {
   function createConnection(host: string, database_name: string, port?: number, options?: ConnectionOption): Connection;
   function disconnect(callback?: (err?: any) => void): Mongoose;
 
-  function model<T extends Document>(name: string, schema: Schema, collection?: string, skipInit?: boolean): Model<T>;
+  function model<T extends Document>(name: string, schema?: Schema, collection?: string, skipInit?: boolean): Model<T>;
   function modelNames(): string[];
   function plugin(plugin: (schema: Schema, options?: Object) => void, options?: Object): Mongoose;
 
@@ -31,7 +31,7 @@ declare module "mongoose" {
     createConnection(host: string, database_name: string, port?: number, options?: ConnectionOption): Connection;
     disconnect(callback?: (err?: any) => void): Mongoose;
     get(key: string): any;
-    model<T extends Document>(name: string, schema: Schema, collection?: string, skipInit?: boolean): Model<T>;
+    model<T extends Document>(name: string, schema?: Schema, collection?: string, skipInit?: boolean): Model<T>;
     modelNames(): string[];
     plugin(plugin: (schema: Schema, options?: Object) => void, options?: Object): Mongoose;
     set(key: string, value: any): void;
@@ -47,7 +47,7 @@ declare module "mongoose" {
 
     close(callback?: (err: any) => void): Connection;
     collection(name: string, options?: Object): Collection;
-    model<T extends Document>(name: string, schema: Schema, collection?: string): Model<T>;
+    model<T extends Document>(name: string, schema?: Schema, collection?: string): Model<T>;
     modelNames(): string[];
     open(host: string, database?: string, port?: number, options?: ConnectionOption, callback?: (err: any) => void): Connection;
     openSet(uris: string, database?: string, options?: ConnectionSetOption, callback?: (err: any) => void): Connection;