diff --git a/main.js b/main.js
index 0553860..16a61f1 100644
--- a/main.js
+++ b/main.js
@@ -73,6 +73,7 @@ const defaultSettings = {
   index: true,
   scan: true,
   unityHack: true,
+  sharedArrayBuffers: false,
   extensions: ['html'],
   recent: [],
 };
diff --git a/src/index.html b/src/index.html
index b4e011a..7c7674c 100644
--- a/src/index.html
+++ b/src/index.html
@@ -43,6 +43,10 @@ <h2>A simple web server for local web development</h2>
                 <label for="unityHack">Support Unity</label>
                 <input type="checkbox" id="unityHack"/>
             </div>
+            <div class="item checkbox">
+                <label for="sharedArrayBuffers">SharedArrayBuffer headers</label>
+                <input type="checkbox" id="sharedArrayBuffers"/>
+            </div>
             <div class="item checkbox">
                 <label for="ssl">Use HTTPS</label>
                 <input type="checkbox" id="ssl"/>
diff --git a/src/index.js b/src/index.js
index f5a9f25..435a3c3 100644
--- a/src/index.js
+++ b/src/index.js
@@ -203,6 +203,7 @@ ipcRenderer.on('stopped', () => {
   startElem.textContent = "Start";
   launchElem.disabled = true;
   log("server stopped");
+  clearQRCodes();
 });
 
 ipcRenderer.send('getSettings');
@@ -283,12 +284,14 @@ function updateSettings() {
 function addQRCode(s) {
   const qr = QrCode.encodeText(s, Ecc.MEDIUM);
   const scale = 4;
-  ctx.canvas.width = qr.size * scale;
-  ctx.canvas.height = qr.size * scale;
+  const padding = 3;
+  const size = qr.size + padding * 2;
+  ctx.canvas.width = size * scale;
+  ctx.canvas.height = size * scale;
   ctx.scale(scale, scale);
-  for (let y = 0; y < qr.size; y++) {
-    for (let x = 0; x < qr.size; x++) {
-      ctx.fillStyle = qr.getModule(x, y) ? 'black' : 'white';
+  for (let y = 0; y < size; y++) {
+    for (let x = 0; x < size; x++) {
+      ctx.fillStyle = qr.getModule(x - padding, y - padding) ? 'black' : 'white';
       ctx.fillRect(x, y, 1, 1);
     }
   }