diff --git a/std/encoding/yaml/dumper/dumper_state.ts b/std/encoding/yaml/dumper/dumper_state.ts
index 30e65f9a79..c2b7608f56 100644
--- a/std/encoding/yaml/dumper/dumper_state.ts
+++ b/std/encoding/yaml/dumper/dumper_state.ts
@@ -62,10 +62,13 @@ export interface DumperStateOptions {
   /** specifies a schema to use. */
   schema?: SchemaDefinition;
   /**
-   * if true, sort keys when dumping YAML.
+   * If true, sort keys when dumping YAML in ascending, ASCII character order.
    * If a function, use the function to sort the keys. (default: false)
+   * If a function is specified, the function must return a negative value
+   * if first argument is less than second argument, zero if they're equal
+   * and a positive value otherwise.
    */
-  sortKeys?: boolean | ((a: Any, b: Any) => number);
+  sortKeys?: boolean | ((a: string, b: string) => number);
   /** set max line width. (default: 80) */
   lineWidth?: number;
   /**