diff --git a/client/src/main/java/org/asynchttpclient/util/HttpUtils.java b/client/src/main/java/org/asynchttpclient/util/HttpUtils.java
index 3cca41e616..e67b699a53 100644
--- a/client/src/main/java/org/asynchttpclient/util/HttpUtils.java
+++ b/client/src/main/java/org/asynchttpclient/util/HttpUtils.java
@@ -24,8 +24,8 @@
 import java.net.URLEncoder;
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
+import java.security.SecureRandom;
 import java.util.List;
-import java.util.concurrent.ThreadLocalRandom;
 
 import static java.nio.charset.StandardCharsets.US_ASCII;
 import static java.nio.charset.StandardCharsets.UTF_8;
@@ -114,9 +114,13 @@ public static String originHeader(Uri uri) {
     // The pool of ASCII chars to be used for generating a multipart boundary.
     private static final byte[] MULTIPART_CHARS = "-_1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".getBytes(US_ASCII);
 
+    // The boundary is what separates parts whose content is not escaped, so it must be unpredictable,
+    // like the cnonce in Realm and the SCRAM nonce.
+    private static final ThreadLocal<SecureRandom> BOUNDARY_RANDOM = ThreadLocal.withInitial(SecureRandom::new);
+
     // a random size from 30 to 40
     public static byte[] computeMultipartBoundary() {
-        ThreadLocalRandom random = ThreadLocalRandom.current();
+        SecureRandom random = BOUNDARY_RANDOM.get();
         byte[] bytes = new byte[random.nextInt(11) + 30];
         for (int i = 0; i < bytes.length; i++) {
             bytes[i] = MULTIPART_CHARS[random.nextInt(MULTIPART_CHARS.length)];
diff --git a/client/src/main/java/org/asynchttpclient/ws/WebSocketUtils.java b/client/src/main/java/org/asynchttpclient/ws/WebSocketUtils.java
index 628cc1d7df..3a20b1691a 100644
--- a/client/src/main/java/org/asynchttpclient/ws/WebSocketUtils.java
+++ b/client/src/main/java/org/asynchttpclient/ws/WebSocketUtils.java
@@ -15,8 +15,7 @@
  */
 package org.asynchttpclient.ws;
 
-import io.netty.util.internal.ThreadLocalRandom;
-
+import java.security.SecureRandom;
 import java.util.Base64;
 
 import static java.nio.charset.StandardCharsets.US_ASCII;
@@ -25,16 +24,16 @@
 public final class WebSocketUtils {
     private static final String MAGIC_GUID = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
 
+    // RFC 6455 section 10.3 requires the handshake nonce to come from a strong source of entropy.
+    private static final ThreadLocal<SecureRandom> KEY_RANDOM = ThreadLocal.withInitial(SecureRandom::new);
+
     private WebSocketUtils() {
         // Prevent outside initialization
     }
 
     public static String getWebSocketKey() {
         byte[] nonce = new byte[16];
-        ThreadLocalRandom random = ThreadLocalRandom.current();
-        for (int i = 0; i < nonce.length; i++) {
-            nonce[i] = (byte) random.nextInt(256);
-        }
+        KEY_RANDOM.get().nextBytes(nonce);
         return Base64.getEncoder().encodeToString(nonce);
     }
 
diff --git a/client/src/test/java/org/asynchttpclient/util/HttpUtilsTest.java b/client/src/test/java/org/asynchttpclient/util/HttpUtilsTest.java
index 57d031498d..eda97ffa4c 100644
--- a/client/src/test/java/org/asynchttpclient/util/HttpUtilsTest.java
+++ b/client/src/test/java/org/asynchttpclient/util/HttpUtilsTest.java
@@ -28,7 +28,9 @@
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 import static io.netty.handler.codec.http.HttpHeaderValues.APPLICATION_JSON;
 import static java.nio.charset.StandardCharsets.ISO_8859_1;
@@ -119,6 +121,20 @@ public void testGetFollowRedirectPriorityGivenToRequest() {
         assertFalse(followRedirect, "Follow redirect value set in request should be given priority");
     }
 
+    @RepeatedIfExceptionsTest(repeats = 5)
+    public void testComputeMultipartBoundary() {
+        String allowed = "-_1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+        Set<String> boundaries = new HashSet<>();
+        for (int i = 0; i < 1000; i++) {
+            String boundary = new String(HttpUtils.computeMultipartBoundary(), US_ASCII);
+            assertTrue(boundary.length() >= 30 && boundary.length() <= 40, "Unexpected boundary length: " + boundary.length());
+            for (int j = 0; j < boundary.length(); j++) {
+                assertTrue(allowed.indexOf(boundary.charAt(j)) != -1, "Illegal boundary char: " + boundary.charAt(j));
+            }
+            assertTrue(boundaries.add(boundary), "Boundary was generated twice: " + boundary);
+        }
+    }
+
     private static void formUrlEncoding(Charset charset) throws Exception {
         String key = "key";
         String value = "中文";