diff --git a/.gitattributes b/.gitattributes
index 64ab6e0..f658344 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,6 +1,6 @@
 /.gitattributes export-ignore
+/.github/ export-ignore
 /.gitignore export-ignore
-/.travis.yml export-ignore
 /examples export-ignore
 /phpunit.xml.dist export-ignore
 /phpunit.xml.legacy export-ignore
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..d321f38
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,45 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  PHPUnit:
+    name: PHPUnit (PHP ${{ matrix.php }})
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        php:
+          - 7.4
+          - 7.3
+          - 7.2
+          - 7.1
+          - 7.0
+          - 5.6
+          - 5.5
+          - 5.4
+          - 5.3
+    steps:
+      - uses: actions/checkout@v2
+      - uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          coverage: xdebug
+      - run: composer install
+      - run: vendor/bin/phpunit --coverage-text
+        if: ${{ matrix.php >= 7.3 }}
+      - run: vendor/bin/phpunit --coverage-text -c phpunit.xml.legacy
+        if: ${{ matrix.php < 7.3 }}
+
+  PHPUnit-hhvm:
+    name: PHPUnit (HHVM)
+    runs-on: ubuntu-18.04
+    continue-on-error: true
+    steps:
+      - uses: actions/checkout@v2
+      - uses: azjezz/setup-hhvm@v1
+        with:
+          version: lts-3.30
+      - run: hhvm $(which composer) install
+      - run: hhvm vendor/bin/phpunit
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index 5623330..0000000
--- a/.travis.yml
+++ /dev/null
@@ -1,27 +0,0 @@
-language: php
-
-# lock distro so new future defaults will not break the build
-dist: trusty
-
-jobs:
-  include:
-    - php: 5.3
-      dist: precise
-    - php: 5.4
-    - php: 5.5
-    - php: 5.6
-    - php: 7.0
-    - php: 7.1
-    - php: 7.2
-    - php: 7.3
-    - php: 7.4
-    - php: hhvm-3.18
-  allow_failures:
-    - php: hhvm-3.18
-
-install:
-  - composer install
-
-script:
-  - if [[ "$TRAVIS_PHP_VERSION" > "7.2" ]]; then vendor/bin/phpunit --coverage-text; fi
-  - if [[ "$TRAVIS_PHP_VERSION" < "7.3" ]]; then vendor/bin/phpunit --coverage-text -c phpunit.xml.legacy; fi
diff --git a/README.md b/README.md
index 837bed0..159459d 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # Datagram
 
-[![Build Status](https://travis-ci.org/reactphp/datagram.svg?branch=master)](https://travis-ci.org/reactphp/datagram)
+[![CI status](https://github.com/reactphp/datagram/workflows/CI/badge.svg)](https://github.com/reactphp/datagram/actions)
 
 Event-driven UDP datagram socket client and server for [ReactPHP](https://reactphp.org).
 
diff --git a/src/Buffer.php b/src/Buffer.php
index dc02953..e5aa2f6 100644
--- a/src/Buffer.php
+++ b/src/Buffer.php
@@ -79,10 +79,6 @@ public function close()
 
     public function end()
     {
-        if ($this->writable === false) {
-            return;
-        }
-
         $this->writable = false;
 
         if (!$this->outgoing) {
diff --git a/src/Socket.php b/src/Socket.php
index 1315d8c..8a1d294 100644
--- a/src/Socket.php
+++ b/src/Socket.php
@@ -102,11 +102,10 @@ private function sanitizeAddress($address)
             return null;
         }
 
-        // this is an IPv6 address which includes colons but no square brackets
+        // check if this is an IPv6 address which includes multiple colons but no square brackets (PHP < 7.3)
         $pos = \strrpos($address, ':');
         if ($pos !== false && \strpos($address, ':') < $pos && \substr($address, 0, 1) !== '[') {
-            $port = \substr($address, $pos + 1);
-            $address = '[' . \substr($address, 0, $pos) . ']:' . $port;
+            $address = '[' . \substr($address, 0, $pos) . ']:' . \substr($address, $pos + 1); // @codeCoverageIgnore
         }
         return $address;
     }
diff --git a/tests/BufferTest.php b/tests/BufferTest.php
new file mode 100644
index 0000000..2149ce4
--- /dev/null
+++ b/tests/BufferTest.php
@@ -0,0 +1,72 @@
+<?php
+
+namespace React\Tests\Datagram;
+
+use PHPUnit\Framework\TestCase;
+use React\Datagram\Buffer;
+
+class BufferTest extends TestCase
+{
+    public function testSendAddsSocketToLoop()
+    {
+        $socket = stream_socket_client('udp://127.0.0.1:8000');
+
+        $loop = $this->getMockBuilder('React\EventLoop\LoopInterface')->getMock();
+        $loop->expects($this->once())->method('addWriteStream')->with($socket);
+
+        $client = new Buffer($loop, $socket);
+
+        $client->send('foo');
+    }
+
+    public function testSendAfterCloseIsNoop()
+    {
+        $loop = $this->getMockBuilder('React\EventLoop\LoopInterface')->getMock();
+        $loop->expects($this->never())->method('addWriteStream');
+
+        $socket = stream_socket_client('udp://127.0.0.1:8000');
+
+        $client = new Buffer($loop, $socket);
+
+        $client->close();
+        $client->send('foo');
+    }
+
+    public function testCloseAfterSendAddsSocketToLoopRemovesSocketFromLoopAgain()
+    {
+        $socket = stream_socket_client('udp://127.0.0.1:8000');
+
+        $loop = $this->getMockBuilder('React\EventLoop\LoopInterface')->getMock();
+        $loop->expects($this->once())->method('addWriteStream')->with($socket);
+        $loop->expects($this->once())->method('removeWriteStream')->with($socket);
+
+        $client = new Buffer($loop, $socket);
+
+        $client->send('foo');
+        $client->close();
+    }
+
+    public function testCloseTwiceEmitsCloseEventOnce()
+    {
+        $loop = $this->getMockBuilder('React\EventLoop\LoopInterface')->getMock();
+
+        $socket = stream_socket_client('udp://127.0.0.1:8000');
+
+        $client = new Buffer($loop, $socket);
+
+        $closed = 0;
+        $client->on('close', function () use (&$closed) {
+            ++$closed;
+        });
+
+        $this->assertEquals(0, $closed);
+
+        $client->close();
+
+        $this->assertEquals(1, $closed);
+
+        $client->close();
+
+        $this->assertEquals(1, $closed);
+    }
+}