diff --git a/types/joi/index.d.ts b/types/joi/index.d.ts
index cc13a9deca..7a41f238de 100644
--- a/types/joi/index.d.ts
+++ b/types/joi/index.d.ts
@@ -1071,7 +1071,7 @@ export function reach<T extends Schema>(schema: ObjectSchema, path: string): T;
 /**
  * Creates a new Joi instance customized with the extension(s) you provide included.
  */
-export function extend(extention: Extension): any;
+export function extend(extension: Extension|Extension[], ...extensions: (Extension|Extension[])[]): any;
 
 // --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---
 
diff --git a/types/joi/joi-tests.ts b/types/joi/joi-tests.ts
index 34fc5271e0..6d2d12efb6 100644
--- a/types/joi/joi-tests.ts
+++ b/types/joi/joi-tests.ts
@@ -970,6 +970,12 @@ const Joi3 = Joi.extend({
     ],
 });
 
+const Joi4 = Joi.extend([{ name: '', base: schema }, { name: '', base: schema }]);
+
+const Joi5 = Joi.extend({ name: '', base: schema }, { name: '', base: schema });
+
+const Joi6 = Joi.extend({ name: '', base: schema }, [{ name: '', base: schema }, { name: '', base: schema }]);
+
 // --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---
 
 const defaultsJoi = Joi.defaults((schema) => {