diff --git a/lib/CachedInputFileSystem.js b/lib/CachedInputFileSystem.js
index e818865..c8d304b 100644
--- a/lib/CachedInputFileSystem.js
+++ b/lib/CachedInputFileSystem.js
@@ -8,8 +8,10 @@
 const nextTick = require("process").nextTick;
 
 /** @typedef {import("./Resolver").FileSystem} FileSystem */
+/** @typedef {import("./Resolver").PathLike} PathLike */
+/** @typedef {import("./Resolver").PathOrFileDescriptor} PathOrFileDescriptor */
 /** @typedef {import("./Resolver").SyncFileSystem} SyncFileSystem */
-/** @typedef {any} BaseFileSystem */
+/** @typedef {FileSystem & SyncFileSystem} BaseFileSystem */
 
 /**
  * @template T
@@ -58,8 +60,8 @@ const runCallbacks = (callbacks, err, result) => {
 
 class OperationMergerBackend {
 	/**
-	 * @param {function} provider async method in filesystem
-	 * @param {function} syncProvider sync method in filesystem
+	 * @param {Function | undefined} provider async method in filesystem
+	 * @param {Function | undefined} syncProvider sync method in filesystem
 	 * @param {BaseFileSystem} providerContext call context for the provider methods
 	 */
 	constructor(provider, syncProvider, providerContext) {
@@ -81,7 +83,7 @@ class OperationMergerBackend {
 						options = undefined;
 					}
 					if (options) {
-						return this._provider.call(
+						return /** @type {Function} */ (this._provider).call(
 							this._providerContext,
 							path,
 							options,
@@ -98,7 +100,8 @@ class OperationMergerBackend {
 						return;
 					}
 					this._activeAsyncOperations.set(path, (callbacks = [callback]));
-					provider(
+					/** @type {Function} */
+					(provider)(
 						path,
 						/**
 						 * @param {Error} err error
@@ -118,7 +121,11 @@ class OperationMergerBackend {
 			   * @returns {any} result
 			   */
 			  (path, options) => {
-					return this._syncProvider.call(this._providerContext, path, options);
+					return /** @type {Function} */ (this._syncProvider).call(
+						this._providerContext,
+						path,
+						options
+					);
 			  }
 			: null;
 	}
@@ -151,11 +158,19 @@ const STORAGE_MODE_IDLE = 0;
 const STORAGE_MODE_SYNC = 1;
 const STORAGE_MODE_ASYNC = 2;
 
+/**
+ * @callback Provide
+ * @param {PathLike | PathOrFileDescriptor} path path
+ * @param {any} options options
+ * @param {FileSystemCallback<any>} callback callback
+ * @returns {void}
+ */
+
 class CacheBackend {
 	/**
 	 * @param {number} duration max cache duration of items
-	 * @param {function} provider async method
-	 * @param {function} syncProvider sync method
+	 * @param {function | undefined} provider async method
+	 * @param {function | undefined} syncProvider sync method
 	 * @param {BaseFileSystem} providerContext call context for the provider methods
 	 */
 	constructor(duration, provider, syncProvider, providerContext) {
@@ -188,7 +203,7 @@ class CacheBackend {
 	}
 
 	/**
-	 * @param {string} path path
+	 * @param {PathLike | PathOrFileDescriptor} path path
 	 * @param {any} options options
 	 * @param {FileSystemCallback<any>} callback callback
 	 * @returns {void}
@@ -203,7 +218,7 @@ class CacheBackend {
 			return;
 		}
 		if (options) {
-			return this._provider.call(
+			return /** @type {Function} */ (this._provider).call(
 				this._providerContext,
 				path,
 				options,
@@ -232,7 +247,8 @@ class CacheBackend {
 		this._activeAsyncOperations.set(path, (callbacks = [callback]));
 
 		// Run the operation
-		this._provider.call(
+		/** @type {Function} */
+		(this._provider).call(
 			this._providerContext,
 			path,
 			/**
@@ -256,7 +272,7 @@ class CacheBackend {
 	}
 
 	/**
-	 * @param {string} path path
+	 * @param {PathLike | PathOrFileDescriptor} path path
 	 * @param {any} options options
 	 * @returns {any} result
 	 */
@@ -265,7 +281,11 @@ class CacheBackend {
 			throw new TypeError("path must be a string");
 		}
 		if (options) {
-			return this._syncProvider.call(this._providerContext, path, options);
+			return /** @type {Function} */ (this._syncProvider).call(
+				this._providerContext,
+				path,
+				options
+			);
 		}
 
 		// In sync mode we may have to decay some cache items
@@ -289,7 +309,10 @@ class CacheBackend {
 		// When in idle mode, we will enter sync mode
 		let result;
 		try {
-			result = this._syncProvider.call(this._providerContext, path);
+			result = /** @type {Function} */ (this._syncProvider).call(
+				this._providerContext,
+				path
+			);
 		} catch (err) {
 			this._storeResult(path, /** @type {Error} */ (err), undefined);
 			this._enterSyncModeWhenIdle();
@@ -449,9 +472,9 @@ class CacheBackend {
  * @template {function} AsyncProvider
  * @template FileSystem
  * @param {number} duration duration in ms files are cached
- * @param {Provider} provider provider
- * @param {AsyncProvider} syncProvider sync provider
- * @param {FileSystem} providerContext provider context
+ * @param {Provider | undefined} provider provider
+ * @param {AsyncProvider | undefined} syncProvider sync provider
+ * @param {BaseFileSystem} providerContext provider context
  * @returns {OperationMergerBackend | CacheBackend} backend
  */
 const createBackend = (duration, provider, syncProvider, providerContext) => {
diff --git a/test/CachedInputFileSystem.test.js b/test/CachedInputFileSystem.test.js
index 913e9ba..2ee1d7c 100644
--- a/test/CachedInputFileSystem.test.js
+++ b/test/CachedInputFileSystem.test.js
@@ -20,6 +20,7 @@ describe("CachedInputFileSystem OperationMergerBackend ('stat' and 'statSync')",
 						100
 					);
 				},
+				// @ts-ignore
 				statSync: function (path, options) {
 					return {
 						path,
@@ -101,6 +102,7 @@ describe("CachedInputFileSystem OperationMergerBackend ('lstat' and 'lstatSync')
 						100
 					);
 				},
+				// @ts-ignore
 				lstatSync: function (path, options) {
 					return {
 						path,
@@ -185,6 +187,7 @@ describe("CachedInputFileSystem OperationMergerBackend ('realpath' and 'realpath
 						100
 					);
 				},
+				// @ts-ignore
 				realpathSync: function (path, options) {
 					return {
 						path,
@@ -269,6 +272,7 @@ describe("CachedInputFileSystem CacheBackend", () => {
 						100
 					);
 				},
+				// @ts-ignore
 				statSync: function (path, options) {
 					return {
 						path,
diff --git a/test/pr-53.test.js b/test/pr-53.test.js
index cc4b7ce..c11db00 100644
--- a/test/pr-53.test.js
+++ b/test/pr-53.test.js
@@ -4,6 +4,7 @@ describe("pr-53", () => {
 	it("should allow to readJsonSync in CachedInputFileSystem", () => {
 		var cfs = new CachedInputFileSystem(
 			{
+				// @ts-ignore
 				readFileSync: function (path) {
 					return JSON.stringify("abc" + path);
 				}
diff --git a/types.d.ts b/types.d.ts
index 43a1b39..6c69f4f 100644
--- a/types.d.ts
+++ b/types.d.ts
@@ -24,6 +24,7 @@ type AliasOptionNewRequest = string | false | string[];
 declare interface AliasOptions {
 	[index: string]: AliasOptionNewRequest;
 }
+type BaseFileSystem = FileSystem & SyncFileSystem;
 declare interface BaseResolveRequest {
 	path: string | false;
 	context?: object;
@@ -52,8 +53,8 @@ type BufferEncoding =
 	| "hex";
 type BufferEncodingOption = "buffer" | { encoding: "buffer" };
 declare class CachedInputFileSystem {
-	constructor(fileSystem: any, duration: number);
-	fileSystem: any;
+	constructor(fileSystem: BaseFileSystem, duration: number);
+	fileSystem: BaseFileSystem;
 	lstat?: LStat;
 	lstatSync?: LStatSync;
 	stat: Stat;
@@ -1025,6 +1026,15 @@ declare interface StatSyncOptions {
 	bigint?: boolean;
 	throwIfNoEntry?: boolean;
 }
+declare interface SyncFileSystem {
+	readFileSync: ReadFileSync;
+	readdirSync: ReaddirSync;
+	readJsonSync?: (arg0: PathOrFileDescriptor) => JsonObject;
+	readlinkSync: ReadlinkSync;
+	lstatSync?: LStatSync;
+	statSync: StatSync;
+	realpathSync?: RealPathSync;
+}
 
 /**
  * `URL` class is a global reference for `require('url').URL`