diff --git a/package-lock.json b/package-lock.json
index b1f724c..435445c 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,14 +1,15 @@
 {
   "name": "httpgd",
-  "version": "0.1.4",
+  "version": "0.1.5",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "httpgd",
-      "version": "0.1.4",
+      "version": "0.1.5",
       "license": "MIT",
       "dependencies": {
+        "@types/ws": "^8.2.0",
         "isomorphic-ws": "^4.0.1"
       },
       "devDependencies": {
@@ -142,12 +143,25 @@
         "@types/unist": "*"
       }
     },
+    "node_modules/@types/node": {
+      "version": "16.11.0",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-16.11.0.tgz",
+      "integrity": "sha512-8MLkBIYQMuhRBQzGN9875bYsOhPnf/0rgXGo66S2FemHkhbn9qtsz9ywV1iCG+vbjigE4WUNVvw37Dx+L0qsPg=="
+    },
     "node_modules/@types/unist": {
       "version": "2.0.6",
       "resolved": "https://registry.npmjs.org/@types/unist/-/unist-2.0.6.tgz",
       "integrity": "sha512-PBjIUxZHOuj0R15/xuwJYjFi+KZdNFrehocChv4g5hu6aFroHue8m0lBP0POdK2nKzbw0cgV1mws8+V/JAcEkQ==",
       "dev": true
     },
+    "node_modules/@types/ws": {
+      "version": "8.2.0",
+      "resolved": "https://registry.npmjs.org/@types/ws/-/ws-8.2.0.tgz",
+      "integrity": "sha512-cyeefcUCgJlEk+hk2h3N+MqKKsPViQgF5boi9TTHSK+PoR9KWBb/C5ccPcDyAqgsbAYHTwulch725DV84+pSpg==",
+      "dependencies": {
+        "@types/node": "*"
+      }
+    },
     "node_modules/@typescript-eslint/eslint-plugin": {
       "version": "4.31.2",
       "resolved": "https://registry.npmjs.org/@typescript-eslint/eslint-plugin/-/eslint-plugin-4.31.2.tgz",
@@ -2162,12 +2176,25 @@
         "@types/unist": "*"
       }
     },
+    "@types/node": {
+      "version": "16.11.0",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-16.11.0.tgz",
+      "integrity": "sha512-8MLkBIYQMuhRBQzGN9875bYsOhPnf/0rgXGo66S2FemHkhbn9qtsz9ywV1iCG+vbjigE4WUNVvw37Dx+L0qsPg=="
+    },
     "@types/unist": {
       "version": "2.0.6",
       "resolved": "https://registry.npmjs.org/@types/unist/-/unist-2.0.6.tgz",
       "integrity": "sha512-PBjIUxZHOuj0R15/xuwJYjFi+KZdNFrehocChv4g5hu6aFroHue8m0lBP0POdK2nKzbw0cgV1mws8+V/JAcEkQ==",
       "dev": true
     },
+    "@types/ws": {
+      "version": "8.2.0",
+      "resolved": "https://registry.npmjs.org/@types/ws/-/ws-8.2.0.tgz",
+      "integrity": "sha512-cyeefcUCgJlEk+hk2h3N+MqKKsPViQgF5boi9TTHSK+PoR9KWBb/C5ccPcDyAqgsbAYHTwulch725DV84+pSpg==",
+      "requires": {
+        "@types/node": "*"
+      }
+    },
     "@typescript-eslint/eslint-plugin": {
       "version": "4.31.2",
       "resolved": "https://registry.npmjs.org/@typescript-eslint/eslint-plugin/-/eslint-plugin-4.31.2.tgz",
diff --git a/package.json b/package.json
index 785fd3a..eba7f00 100644
--- a/package.json
+++ b/package.json
@@ -43,6 +43,7 @@
     "lib/**/*"
   ],
   "dependencies": {
+    "@types/ws": "^8.2.0",
     "isomorphic-ws": "^4.0.1"
   }
 }
diff --git a/src/api.ts b/src/api.ts
index ec7d278..c1e0119 100644
--- a/src/api.ts
+++ b/src/api.ts
@@ -6,7 +6,7 @@ import {
   HttpgdPlotRequest,
   HttpgdRemoveRequest
 } from './types';
-import WebSocket = require('isomorphic-ws');
+import { WebSocket } from 'isomorphic-ws';
 
 const URL_HTTP = 'http://';
 const URL_WS = 'ws://';
diff --git a/src/connection.ts b/src/connection.ts
index 74d22b3..49098cd 100644
--- a/src/connection.ts
+++ b/src/connection.ts
@@ -1,7 +1,7 @@
 import { HttpgdBackend, HttpgdStateResponse } from './types';
 import * as api from './api';
 import { StateChangeListener } from './utils';
-import WebSocket = require('isomorphic-ws');
+import { WebSocket } from 'isomorphic-ws';
 
 /**
  * Connection mode.
@@ -108,7 +108,7 @@ export class HttpgdConnection {
         this.clearWebsocket();
 
         this.socket = api.new_websocket(this.backend);
-        this.socket.onmessage = (ev) => this.onWsMessage(ev.data);
+        this.socket.onmessage = (ev) => this.onWsMessage(ev.data.toString());
         this.socket.onopen = () => this.onWsOpen();
         this.socket.onclose = () => this.onWsClose();
         this.socket.onerror = () => this.start(HttpgdConnectionMode.SLOWPOLL);
diff --git a/tsconfig.json b/tsconfig.json
index 8205908..e25b774 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -4,7 +4,8 @@
     "module": "commonjs",
     "declaration": true,
     "outDir": "./lib",
-    "strict": true
+    "strict": true,
+    "esModuleInterop": true
   },
   "include": [
     "src"