diff --git a/src/handler.ts b/src/handler.ts
index 33118e54..840e0a47 100644
--- a/src/handler.ts
+++ b/src/handler.ts
@@ -11,15 +11,15 @@ export type Path = string;
 export const STR_DATA = 'data';
 export const STR_END = 'end';
 export const STR_CLOSE = 'close';
-export const EMPTY_FN = () => {};
-export const IDENTITY_FN = (val: unknown) => val;
+export const EMPTY_FN = (): void => {};
+export const IDENTITY_FN = (val: unknown): unknown => val;
 
 const pl = process.platform;
-export const isWindows = pl === 'win32';
-export const isMacos = pl === 'darwin';
-export const isLinux = pl === 'linux';
-export const isFreeBSD = pl === 'freebsd';
-export const isIBMi = osType() === 'OS400';
+export const isWindows: boolean = pl === 'win32';
+export const isMacos: boolean = pl === 'darwin';
+export const isLinux: boolean = pl === 'linux';
+export const isFreeBSD: boolean = pl === 'freebsd';
+export const isIBMi: boolean = osType() === 'OS400';
 
 export const EVENTS = {
   ALL: 'all',
@@ -375,7 +375,10 @@ export class NodeFsHandler {
    * @param listener on fs change
    * @returns closer for the watcher instance
    */
-  _watchWithNodeFs(path: string, listener: (path: string, newStats?: any) => void | Promise<void>) {
+  _watchWithNodeFs(
+    path: string,
+    listener: (path: string, newStats?: any) => void | Promise<void>
+  ): (() => void) | undefined {
     const opts = this.fsw.options;
     const directory = sysPath.dirname(path);
     const basename = sysPath.basename(path);
@@ -532,7 +535,7 @@ export class NodeFsHandler {
     dir: Path,
     depth: number,
     throttler: Throttler
-  ) {
+  ): Promise<unknown> | undefined {
     // Normalize the directory name on Windows
     directory = sysPath.join(directory, '');
 
@@ -677,7 +680,7 @@ export class NodeFsHandler {
     priorWh: WatchHelper | undefined,
     depth: number,
     target?: string
-  ) {
+  ): Promise<string | false | undefined> {
     const ready = this.fsw._emitReady;
     if (this.fsw._isIgnored(path) || this.fsw.closed) {
       ready();
diff --git a/src/index.ts b/src/index.ts
index 46b4bc92..14006da6 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -214,13 +214,13 @@ class DirEntry {
     this.items = new Set<Path>();
   }
 
-  add(item: string) {
+  add(item: string): void {
     const { items } = this;
     if (!items) return;
     if (item !== ONE_DOT && item !== TWO_DOTS) items.add(item);
   }
 
-  async remove(item: string) {
+  async remove(item: string): Promise<void> {
     const { items } = this;
     if (!items) return;
     items.delete(item);
@@ -236,7 +236,7 @@ class DirEntry {
     }
   }
 
-  has(item: string) {
+  has(item: string): boolean | undefined {
     const { items } = this;
     if (!items) return;
     return items.has(item);
@@ -248,7 +248,7 @@ class DirEntry {
     return [...items.values()];
   }
 
-  dispose() {
+  dispose(): void {
     this.items.clear();
     this.path = '';
     this._removeWatcher = EMPTY_FN;
@@ -581,7 +581,7 @@ export class FSWatcher extends EventEmitter<FSWatcherEventMap> {
     return watchList;
   }
 
-  emitWithAll(event: EventName, args: EmitArgs) {
+  emitWithAll(event: EventName, args: EmitArgs): void {
     this.emit(event, ...args);
     if (event !== EV.ERROR) this.emit(EV.ALL, event, ...args);
   }
@@ -597,7 +597,7 @@ export class FSWatcher extends EventEmitter<FSWatcherEventMap> {
    * @param stats arguments to be passed with event
    * @returns the error if defined, otherwise the value of the FSWatcher instance's `closed` flag
    */
-  async _emit(event: EventName, path: Path, stats?: Stats) {
+  async _emit(event: EventName, path: Path, stats?: Stats): Promise<this | undefined> {
     if (this.closed) return;
 
     const opts = this.options;
@@ -735,7 +735,7 @@ export class FSWatcher extends EventEmitter<FSWatcherEventMap> {
     return thr;
   }
 
-  _incrReadyCount() {
+  _incrReadyCount(): number {
     return this._readyCount++;
   }
 
@@ -752,7 +752,7 @@ export class FSWatcher extends EventEmitter<FSWatcherEventMap> {
     threshold: number,
     event: EventName,
     awfEmit: (err?: Error, stat?: Stats) => void
-  ) {
+  ): void {
     const awf = this.options.awaitWriteFinish;
     if (typeof awf !== 'object') return;
     const pollInterval = awf.pollInterval as unknown as number;
@@ -821,7 +821,7 @@ export class FSWatcher extends EventEmitter<FSWatcherEventMap> {
     return this._userIgnored(path, stats);
   }
 
-  _isntIgnored(path: Path, stat?: Stats) {
+  _isntIgnored(path: Path, stat?: Stats): boolean {
     return !this._isIgnored(path, stat);
   }
 
@@ -926,7 +926,7 @@ export class FSWatcher extends EventEmitter<FSWatcherEventMap> {
   /**
    * Closes all watchers for a path
    */
-  _closePath(path: Path) {
+  _closePath(path: Path): void {
     this._closeFile(path);
     const dir = sysPath.dirname(path);
     this._getWatchedDir(dir).remove(sysPath.basename(path));
@@ -935,14 +935,14 @@ export class FSWatcher extends EventEmitter<FSWatcherEventMap> {
   /**
    * Closes only file-specific watchers
    */
-  _closeFile(path: Path) {
+  _closeFile(path: Path): void {
     const closers = this._closers.get(path);
     if (!closers) return;
     closers.forEach((closer) => closer());
     this._closers.delete(path);
   }
 
-  _addPathCloser(path: Path, closer: () => void) {
+  _addPathCloser(path: Path, closer: () => void): void {
     if (!closer) return;
     let list = this._closers.get(path);
     if (!list) {
@@ -952,7 +952,7 @@ export class FSWatcher extends EventEmitter<FSWatcherEventMap> {
     list.push(closer);
   }
 
-  _readdirp(root: Path, opts?: Partial<ReaddirpOptions>) {
+  _readdirp(root: Path, opts?: Partial<ReaddirpOptions>): ReaddirpStream | undefined {
     if (this.closed) return;
     const options = { type: EV.ALL, alwaysStat: true, lstat: true, ...opts, depth: 0 };
     let stream: ReaddirpStream | undefined = readdirp(root, options);
@@ -985,4 +985,4 @@ export function watch(paths: string | string[], options: ChokidarOptions = {}):
   return watcher;
 }
 
-export default { watch, FSWatcher };
+export default { watch: watch as typeof watch, FSWatcher: FSWatcher as typeof FSWatcher };
diff --git a/tsconfig.esm.json b/tsconfig.esm.json
index 3ca59b38..ac719249 100644
--- a/tsconfig.esm.json
+++ b/tsconfig.esm.json
@@ -7,7 +7,8 @@
     "moduleResolution": "bundler",
     "noImplicitReturns": false,
     "sourceMap": false,
-    "declarationMap": false
+    "declarationMap": false,
+    "isolatedDeclarations": true
   },
   "include": [
     "src"
diff --git a/tsconfig.json b/tsconfig.json
index c9932bcd..370ee502 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -5,7 +5,8 @@
     "outDir": ".",
     "noImplicitReturns": false,
     "sourceMap": false,
-    "declarationMap": false
+    "declarationMap": false,
+    "isolatedDeclarations": true
   },
   "include": [
     "src"