diff --git a/Example/CompleteNotificationExample.php b/Example/CompleteNotificationExample.php
index e62d6ca..0334460 100644
--- a/Example/CompleteNotificationExample.php
+++ b/Example/CompleteNotificationExample.php
@@ -12,6 +12,7 @@
 namespace Serhiy\Pushover\Example;
 
 use Serhiy\Pushover\Api\Message\Attachment;
+use Serhiy\Pushover\Api\Message\CustomSound;
 use Serhiy\Pushover\Api\Message\Message;
 use Serhiy\Pushover\Api\Message\Notification;
 use Serhiy\Pushover\Api\Message\Priority;
@@ -48,8 +49,10 @@ public function completeNotification()
 
         // create notification
         $notification = new Notification($application, $recipient, $message);
-        // set notification sound
+        // set notification built-in sound
         $notification->setSound(new Sound(Sound::PUSHOVER));
+        // or set notification custom sound
+        $notification->setCustomSound(new CustomSound("door_open"));
         // add attachment
         $notification->setAttachment(new Attachment("/path/to/file.jpg", Attachment::MIME_TYPE_JPEG));
 
diff --git a/README.md b/README.md
index 8f2ef17..35876b5 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,7 @@ Light, simple and fast, yet comprehensive wrapper for the [Pushover](https://pus
   - HTML messages
   - Supplementary URL and its title
   - Notification priority
-  - Notification sound
+  - Notification sound (including custom sound)
   - Message time
 - User/Group Validation API ([Example](Example/UserGroupValidationExample.php))
   - Validation by user or group key
diff --git a/src/Api/Message/CustomSound.php b/src/Api/Message/CustomSound.php
new file mode 100644
index 0000000..5393ac9
--- /dev/null
+++ b/src/Api/Message/CustomSound.php
@@ -0,0 +1,60 @@
+<?php
+
+/*
+ * This file is part of the Pushover package.
+ *
+ * (c) Serhiy Lunak <https://github.com/slunak>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Serhiy\Pushover\Api\Message;
+
+use Serhiy\Pushover\Exception\InvalidArgumentException;
+
+/**
+ * @author Serhiy Lunak
+ */
+class CustomSound
+{
+    /**
+     * Custom Sound Notification
+     * Admins can now upload custom sounds through Pushover website and have them played on devices
+     * without having to copy sound files to each device. Can only contain letters, numbers, underscores, and dashes,
+     * and is limited to 20 characters, such as "warning", "door_open", or "long_siren2". It cannot match the name
+     * of any built-in sound and will be specified as the sound parameter through our API when requesting this sound.
+     *
+     * @var string
+     */
+    private $customSound;
+
+    public function __construct(string $customSound)
+    {
+        $this->setCustomSound($customSound);
+    }
+
+    /**
+     * @return string
+     */
+    public function getCustomSound(): string
+    {
+        return $this->customSound;
+    }
+
+    /**
+     * @param string $customSound
+     */
+    public function setCustomSound(string $customSound): void
+    {
+        if (in_array($customSound, Sound::getAvailableSounds())) {
+            throw new InvalidArgumentException(sprintf('Sound "%s" is not a valid custom sound because it matches the name of a built-in sound.', $customSound));
+        }
+
+        if (1 !== preg_match("/^[a-zA-Z0-9_-]{1,20}$/", $customSound)) {
+            throw new InvalidArgumentException(sprintf('Sound "%s" is not a valid custom sound. Custom sound name can only contain letters, numbers, underscores, and dashes, and is limited to 20 characters, such as "warning", "door_open", or "long_siren2".', $customSound));
+        }
+
+        $this->customSound = $customSound;
+    }
+}
diff --git a/src/Api/Message/Notification.php b/src/Api/Message/Notification.php
index 3a63fa2..555f4fb 100644
--- a/src/Api/Message/Notification.php
+++ b/src/Api/Message/Notification.php
@@ -47,6 +47,11 @@ class Notification
      */
     private $sound;
 
+    /**
+     * @var CustomSound|null
+     */
+    private $customSound;
+
     /**
      * @var Attachment|null
      */
@@ -123,6 +128,22 @@ public function setSound(?Sound $sound): void
         $this->sound = $sound;
     }
 
+    /**
+     * @return CustomSound|null
+     */
+    public function getCustomSound(): ?CustomSound
+    {
+        return $this->customSound;
+    }
+
+    /**
+     * @param CustomSound|null $customSound
+     */
+    public function setCustomSound(?CustomSound $customSound): void
+    {
+        $this->customSound = $customSound;
+    }
+
     /**
      * @return Attachment|null
      */
diff --git a/src/Client/MessageClient.php b/src/Client/MessageClient.php
index f9972f7..13a9d26 100644
--- a/src/Client/MessageClient.php
+++ b/src/Client/MessageClient.php
@@ -92,6 +92,10 @@ public function buildCurlPostFields(Notification $notification): array
             $curlPostFields['sound'] = $notification->getSound()->getSound();
         }
 
+        if (null !== $notification->getCustomSound()) {
+            $curlPostFields['sound'] = $notification->getCustomSound()->getCustomSound();
+        }
+
         if (null !== $notification->getAttachment()) {
             if (! is_readable($notification->getAttachment()->getFilename())) {
                 throw new LogicException(sprintf('File "%s" does not exist or is not readable.', $notification->getAttachment()->getFilename()));
diff --git a/tests/Api/Message/CustomSoundTest.php b/tests/Api/Message/CustomSoundTest.php
new file mode 100644
index 0000000..5c8ae02
--- /dev/null
+++ b/tests/Api/Message/CustomSoundTest.php
@@ -0,0 +1,90 @@
+<?php
+
+/*
+ * This file is part of the Pushover package.
+ *
+ * (c) Serhiy Lunak <https://github.com/slunak>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Api\Message;
+
+use PHPUnit\Framework\TestCase;
+use Serhiy\Pushover\Api\Message\CustomSound;
+use Serhiy\Pushover\Exception\InvalidArgumentException;
+
+/**
+ * @author Serhiy Lunak
+ */
+class CustomSoundTest extends TestCase
+{
+    public function testCanBeCreated()
+    {
+        $this->assertInstanceOf(CustomSound::class, $customSound = new CustomSound("door_open"));
+
+        return $customSound;
+    }
+
+    /**
+     * @depends testCanBeCreated
+     * @param CustomSound $customSound
+     */
+    public function testGetCustomSound(CustomSound $customSound)
+    {
+        $this->assertEquals('door_open', $customSound->getCustomSound());
+    }
+
+    /**
+     * @depends testCanBeCreated
+     * @param CustomSound $customSound
+     */
+    public function testSetCustomSound(CustomSound $customSound)
+    {
+        $customSound->setCustomSound("warning");
+
+        $this->assertEquals('warning', $customSound->getCustomSound());
+
+        $customSound->setCustomSound("door_open");
+
+        $this->assertEquals('door_open', $customSound->getCustomSound());
+
+        $customSound->setCustomSound("bell-sound");
+
+        $this->assertEquals('bell-sound', $customSound->getCustomSound());
+    }
+
+    /**
+     * @depends testCanBeCreated
+     * @param CustomSound $customSound
+     */
+    public function testSetExistingCustomSound(CustomSound $customSound)
+    {
+        $this->expectException(InvalidArgumentException::class);
+
+        $customSound->setCustomSound("echo");
+    }
+
+    /**
+     * @depends testCanBeCreated
+     * @param CustomSound $customSound
+     */
+    public function testSetInvalidCustomSound(CustomSound $customSound)
+    {
+        $this->expectException(InvalidArgumentException::class);
+
+        $customSound->setCustomSound("warning+door_open");
+    }
+
+    /**
+     * @depends testCanBeCreated
+     * @param CustomSound $customSound
+     */
+    public function testSetLongCustomSound(CustomSound $customSound)
+    {
+        $this->expectException(InvalidArgumentException::class);
+
+        $customSound->setCustomSound("warning_door_open_warning_door_open");
+    }
+}
diff --git a/tests/Api/Message/NotificationTest.php b/tests/Api/Message/NotificationTest.php
index 57bdc25..5876422 100644
--- a/tests/Api/Message/NotificationTest.php
+++ b/tests/Api/Message/NotificationTest.php
@@ -13,6 +13,7 @@
 
 use PHPUnit\Framework\TestCase;
 use Serhiy\Pushover\Api\Message\Attachment;
+use Serhiy\Pushover\Api\Message\CustomSound;
 use Serhiy\Pushover\Api\Message\Message;
 use Serhiy\Pushover\Api\Message\Notification;
 use Serhiy\Pushover\Api\Message\Sound;
@@ -61,6 +62,28 @@ public function testSetSoundNull(Notification $notification)
         $this->assertNull($notification->getSound());
     }
 
+    /**
+     * @depends testCanBeCreated
+     * @param Notification $notification
+     */
+    public function testSetCustomSound(Notification $notification)
+    {
+        $notification->setCustomSound(new CustomSound("door_open"));
+
+        $this->assertEquals('door_open', $notification->getCustomSound()->getCustomSound());
+    }
+
+    /**
+     * @depends testCanBeCreated
+     * @param Notification $notification
+     */
+    public function testSetCustomSoundNull(Notification $notification)
+    {
+        $notification->setCustomSound(null);
+
+        $this->assertNull($notification->getCustomSound());
+    }
+
     /**
      * @depends testCanBeCreated
      * @param Notification $notification