diff --git a/typescript/option/src/helpers/withDefault.ts b/typescript/option/src/helpers/withDefault.ts
index b1c9934..ca855db 100644
--- a/typescript/option/src/helpers/withDefault.ts
+++ b/typescript/option/src/helpers/withDefault.ts
@@ -2,6 +2,12 @@ import { match } from './match'
 import { identity } from '@thi.ng/compose'
 import { Option } from '../types'
 
+/**
+ * Provide a default value, turning an optional value into a normal value.
+ *
+ * @param _default The default value to use.
+ * @param option The option to get the default of.
+ */
 export const withDefault = <T>(_default: T, option: Option<T>) => {
     return match(identity, _default, option)
 }