diff --git a/types/sequelize/index.d.ts b/types/sequelize/index.d.ts
index a9b59a0766..74be4db7c3 100644
--- a/types/sequelize/index.d.ts
+++ b/types/sequelize/index.d.ts
@@ -3865,8 +3865,8 @@ declare namespace sequelize {
          * Search for a single instance by its primary key. This applies LIMIT 1, so the listener will
          * always be called with a single instance.
          */
-        findById<TCustomAttributes>(identifier?: number | string, options?: FindOptions<TAttributes & TCustomAttributes>): Promise<TInstance | null>;
-        findByPrimary<TCustomAttributes>(identifier?: number | string, options?: FindOptions<TAttributes & TCustomAttributes>): Promise<TInstance | null>;
+        findById<TCustomAttributes>(identifier?: number | string | Buffer, options?: FindOptions<TAttributes & TCustomAttributes>): Promise<TInstance | null>;
+        findByPrimary<TCustomAttributes>(identifier?: number | string | Buffer, options?: FindOptions<TAttributes & TCustomAttributes>): Promise<TInstance | null>;
 
         /**
          * Search for a single instance. This applies LIMIT 1, so the listener will always be called with a single
diff --git a/types/sequelize/sequelize-tests.ts b/types/sequelize/sequelize-tests.ts
index f99988b29f..fb49abd88e 100644
--- a/types/sequelize/sequelize-tests.ts
+++ b/types/sequelize/sequelize-tests.ts
@@ -957,6 +957,12 @@ User.findAll( { where: { $or:[ { username: { $not: "user" } }, { theDate: new Da
 User.findAll( { where: { emails: { $overlap: ["me@mail.com", "you@mail.com"] } } } );
 
 User.findById( 'a string' );
+User.findById( 42 );
+User.findById( Buffer.from('a buffer') );
+
+User.findByPrimary( 'a string' );
+User.findByPrimary( 42 );
+User.findByPrimary( Buffer.from('a buffer') );
 
 User.findOne( { where : { username : 'foo' } } );
 User.findOne( { where : { id : 1 }, attributes : ['id', ['username', 'name']] } );