diff --git a/lib/sender.js b/lib/sender.js
index 4490a623b..25df14cde 100644
--- a/lib/sender.js
+++ b/lib/sender.js
@@ -4,7 +4,7 @@
 
 const net = require('net');
 const tls = require('tls');
-const { randomFillSync } = require('crypto');
+const { randomBytes } = require('crypto');
 
 const PerMessageDeflate = require('./permessage-deflate');
 const { EMPTY_BUFFER } = require('./constants');
@@ -13,6 +13,22 @@ const { mask: applyMask, toBuffer } = require('./buffer-util');
 
 const mask = Buffer.alloc(4);
 
+const RANDOM_POOL_SIZE = 8192;
+const RANDOM_POOL_REFRESH = 1024;
+
+let randomPool = Buffer.alloc(0);
+let randomPoolIdx = 0;
+let randomPending = true;
+
+function onRandomBytes(err, buf) {
+  randomPending = false;
+  if (!err) {
+    randomPool = buf;
+    randomPoolIdx = 0;
+  }
+}
+randomBytes(RANDOM_POOL_SIZE, onRandomBytes);
+
 /**
  * HyBi Sender implementation.
  */
@@ -81,13 +97,24 @@ class Sender {
 
     if (!options.mask) return [target, data];
 
-    randomFillSync(mask, 0, 4);
+    if (randomPool.length - randomPoolIdx < 4) {
+      randomPool = randomBytes(32);
+      randomPoolIdx = 0;
+    }
 
     target[1] |= 0x80;
-    target[offset - 4] = mask[0];
-    target[offset - 3] = mask[1];
-    target[offset - 2] = mask[2];
-    target[offset - 1] = mask[3];
+    target[offset - 4] = mask[0] = randomPool[randomPoolIdx++];
+    target[offset - 3] = mask[1] = randomPool[randomPoolIdx++];
+    target[offset - 2] = mask[2] = randomPool[randomPoolIdx++];
+    target[offset - 1] = mask[3] = randomPool[randomPoolIdx++];
+
+    if (
+      !randomPending &&
+      randomPool.length - randomPoolIdx < RANDOM_POOL_REFRESH
+    ) {
+      randomPending = true;
+      randomBytes(RANDOM_POOL_SIZE, onRandomBytes);
+    }
 
     if (merge) {
       applyMask(data, mask, target, offset, data.length);