diff --git a/lib/Resolver.js b/lib/Resolver.js
index 875b435f..93951440 100644
--- a/lib/Resolver.js
+++ b/lib/Resolver.js
@@ -45,10 +45,18 @@ const {
  * @param {T=} result
  */
 
+/** @typedef {function((NodeJS.ErrnoException | null)=, (string | Buffer)[] | IDirent[]=): void} DirentArrayCallback */
+
+/**
+ * @typedef {Object} ReaddirOptions
+ * @property {BufferEncoding | null | 'buffer'} [encoding]
+ * @property {boolean | undefined} [withFileTypes=false]
+ */
+
 /**
  * @typedef {Object} FileSystem
  * @property {(function(string, FileSystemCallback<Buffer | string>): void) & function(string, object, FileSystemCallback<Buffer | string>): void} readFile
- * @property {(function(string, FileSystemCallback<(Buffer | string)[] | FileSystemDirent[]>): void) & function(string, object, FileSystemCallback<(Buffer | string)[] | FileSystemDirent[]>): void} readdir
+ * @property {function(string, (ReaddirOptions | BufferEncoding | null | undefined | 'buffer' | DirentArrayCallback)=,  DirentArrayCallback=): void} readdir
  * @property {((function(string, FileSystemCallback<object>): void) & function(string, object, FileSystemCallback<object>): void)=} readJson
  * @property {(function(string, FileSystemCallback<Buffer | string>): void) & function(string, object, FileSystemCallback<Buffer | string>): void} readlink
  * @property {(function(string, FileSystemCallback<FileSystemStats>): void) & function(string, object, FileSystemCallback<Buffer | string>): void=} lstat
diff --git a/types.d.ts b/types.d.ts
index 01436533..2c0b668e 100644
--- a/types.d.ts
+++ b/types.d.ts
@@ -45,17 +45,31 @@ declare class CachedInputFileSystem {
 		): void;
 	};
 	statSync: (arg0: string, arg1?: object) => FileSystemStats;
-	readdir: {
-		(
-			arg0: string,
-			arg1: FileSystemCallback<(string | Buffer)[] | FileSystemDirent[]>
-		): void;
-		(
-			arg0: string,
-			arg1: object,
-			arg2: FileSystemCallback<(string | Buffer)[] | FileSystemDirent[]>
-		): void;
-	};
+	readdir: (
+		arg0: string,
+		arg1?:
+			| null
+			| ((
+					arg0?: null | NodeJS.ErrnoException,
+					arg1?: (string | Buffer)[] | any[]
+			  ) => void)
+			| ReaddirOptions
+			| "ascii"
+			| "utf8"
+			| "utf-8"
+			| "utf16le"
+			| "ucs2"
+			| "ucs-2"
+			| "base64"
+			| "latin1"
+			| "binary"
+			| "hex"
+			| "buffer",
+		arg2?: (
+			arg0?: null | NodeJS.ErrnoException,
+			arg1?: (string | Buffer)[] | any[]
+		) => void
+	) => void;
 	readdirSync: (
 		arg0: string,
 		arg1?: object
@@ -107,17 +121,31 @@ declare interface FileSystem {
 			arg2: FileSystemCallback<string | Buffer>
 		): void;
 	};
-	readdir: {
-		(
-			arg0: string,
-			arg1: FileSystemCallback<(string | Buffer)[] | FileSystemDirent[]>
-		): void;
-		(
-			arg0: string,
-			arg1: object,
-			arg2: FileSystemCallback<(string | Buffer)[] | FileSystemDirent[]>
-		): void;
-	};
+	readdir: (
+		arg0: string,
+		arg1?:
+			| null
+			| ((
+					arg0?: null | NodeJS.ErrnoException,
+					arg1?: (string | Buffer)[] | any[]
+			  ) => void)
+			| ReaddirOptions
+			| "ascii"
+			| "utf8"
+			| "utf-8"
+			| "utf16le"
+			| "ucs2"
+			| "ucs-2"
+			| "base64"
+			| "latin1"
+			| "binary"
+			| "hex"
+			| "buffer",
+		arg2?: (
+			arg0?: null | NodeJS.ErrnoException,
+			arg1?: (string | Buffer)[] | any[]
+		) => void
+	) => void;
 	readJson?: {
 		(arg0: string, arg1: FileSystemCallback<object>): void;
 		(arg0: string, arg1: object, arg2: FileSystemCallback<object>): void;
@@ -185,6 +213,22 @@ declare interface PossibleFileSystemError {
 	path?: string;
 	syscall?: string;
 }
+declare interface ReaddirOptions {
+	encoding?:
+		| null
+		| "ascii"
+		| "utf8"
+		| "utf-8"
+		| "utf16le"
+		| "ucs2"
+		| "ucs-2"
+		| "base64"
+		| "latin1"
+		| "binary"
+		| "hex"
+		| "buffer";
+	withFileTypes?: boolean;
+}
 
 /**
  * Resolve context