diff --git a/typings/index.d.ts b/typings/index.d.ts
index d1a89d8c2..0a53fdf79 100644
--- a/typings/index.d.ts
+++ b/typings/index.d.ts
@@ -159,8 +159,9 @@ declare namespace commander {
      *
      * @returns Command for chaining
      */
-    option(flags: string, description?: string, fn?: ((arg1: any, arg2: any) => void) | RegExp, defaultValue?: any): Command;
-    option(flags: string, description?: string, defaultValue?: any): Command;
+    option(flags: string, description?: string, defaultValue?: string | boolean): Command;
+    option(flags: string, description: string, regexp: RegExp, defaultValue?: string | boolean): Command;
+    option<T>(flags: string, description: string, fn: (value: string, previous: T) => T, defaultValue?: T): Command;
 
     /**
      * Define a required option, which must have a value after parsing. This usually means
@@ -168,8 +169,9 @@ declare namespace commander {
      *
      * The `flags` string should contain both the short and long flags, separated by comma, a pipe or space.
      */
-    requiredOption(flags: string, description?: string, fn?: ((arg1: any, arg2: any) => void) | RegExp, defaultValue?: any): Command;
-    requiredOption(flags: string, description?: string, defaultValue?: any): Command;
+    requiredOption(flags: string, description?: string, defaultValue?: string | boolean): Command;
+    requiredOption(flags: string, description: string, regexp: RegExp, defaultValue?: string | boolean): Command;
+    requiredOption<T>(flags: string, description: string, fn: (value: string, previous: T) => T, defaultValue?: T): Command;
 
 
     /**