diff --git a/dom/network/TCPSocket.cpp b/dom/network/TCPSocket.cpp
index ef8e80420e1b..9af1e6f702db 100644
--- a/dom/network/TCPSocket.cpp
+++ b/dom/network/TCPSocket.cpp
@@ -893,9 +893,12 @@ nsresult TCPSocket::ResolveProxy() {
 
   nsCOMPtr<nsIURI> uri;
   nsCString spec = mSsl ? "https://"_ns : "http://"_ns;
+  bool maybeIPv6 = mHost.FindChar(':') != -1;
+  if (maybeIPv6) spec.Append('[');
   if (!AppendUTF16toUTF8(mHost, spec, fallible)) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
+  if (maybeIPv6) spec.Append(']');
   rv = NS_MutateURI(NS_STANDARDURLMUTATOR_CONTRACTID)
            .SetSpec(spec)
            .SetPort(mPort)
diff --git a/dom/network/tests/test_tcpsocket_client_and_server_basics.js b/dom/network/tests/test_tcpsocket_client_and_server_basics.js
index 653f543bc524..79f431cecaa5 100644
--- a/dom/network/tests/test_tcpsocket_client_and_server_basics.js
+++ b/dom/network/tests/test_tcpsocket_client_and_server_basics.js
@@ -589,3 +589,26 @@ async function test_basics() {
 }
 
 add_task(test_basics);
+
+/**
+ * Test that TCPSocket works with ipv6 address.
+ */
+add_task(async function test_ipv6() {
+  const { HttpServer } = ChromeUtils.import(
+    "resource://testing-common/httpd.js"
+  );
+  let deferred = defer();
+  let serverPort = 8086;
+  let httpServer = new HttpServer();
+  httpServer.start_ipv6(serverPort);
+  let clientSocket = new TCPSocket("::1", serverPort);
+  clientSocket.onopen = () => {
+    ok(true, "Connect to ipv6 address succeeded");
+    deferred.resolve();
+  };
+  clientSocket.onerror = () => {
+    ok(false, "Connect to ipv6 address failed");
+    deferred.reject();
+  };
+  return deferred.promise;
+});