diff --git a/src/main/php/img/io/AvifStreamReader.class.php b/src/main/php/img/io/AvifStreamReader.class.php
new file mode 100755
index 00000000..83070462
--- /dev/null
+++ b/src/main/php/img/io/AvifStreamReader.class.php
@@ -0,0 +1,29 @@
+<?php namespace img\io;
+
+use img\ImagingException;
+
+/**
+ * Reads Avif from an image
+ *
+ * @ext   gd
+ * @see   https://www.php.net/manual/en/function.imagecreatefromavif.php
+ * @see   img.io.StreamReader
+ */
+class AvifStreamReader extends StreamReader implements UriReader {
+
+  /**
+   * Read image
+   *
+   * @param   string uri
+   * @return  resource
+   * @throws  img.ImagingException
+   */
+  public function readImageFromUri($uri) {
+    if (false === ($r= imagecreatefromavif($uri))) {
+      $e= new ImagingException('Cannot read image from "'.$uri.'"');
+      \xp::gc(__FILE__);
+      throw $e;
+    }
+    return $r;
+  }
+}
\ No newline at end of file
diff --git a/src/main/php/img/io/AvifStreamWriter.class.php b/src/main/php/img/io/AvifStreamWriter.class.php
new file mode 100755
index 00000000..0a859857
--- /dev/null
+++ b/src/main/php/img/io/AvifStreamWriter.class.php
@@ -0,0 +1,45 @@
+<?php namespace img\io;
+
+/**
+ * Writes Avif to a stream
+ *
+ * @ext   gd
+ * @see   https://www.php.net/manual/en/function.imageavif.php
+ * @see   img.io.StreamWriter
+ */
+class AvifStreamWriter extends StreamWriter {
+  public $quality;
+  
+  /**
+   * Constructor
+   *
+   * @param   io.Stream stream
+   * @param   int quality default -1
+   */
+  public function __construct($stream, $quality= -1) {
+    parent::__construct($stream);
+    $this->quality= $quality;
+  }
+
+  /**
+   * Output an image
+   *
+   * @param   resource handle
+   * @return  bool
+   */    
+  public function output($handle) {
+    if (imageistruecolor($handle)) return imageavif($handle, null, $this->quality);
+
+    // Prevent "imageavif(): avif error - avif doesn't support palette images"
+    $width= imagesx($handle);
+    $height= imagesy($handle);
+    $copy= imagecreatetruecolor($width, $height);
+    imagecopy($copy, $handle, 0, 0, 0, 0, $width, $height);
+
+    try {
+      return imageavif($copy, null, $this->quality);
+    } finally {
+      PHP_VERSION_ID <= 80000 && imagedestroy($copy);
+    }
+  }
+}
\ No newline at end of file
diff --git a/src/test/php/img/unittest/AvifImageReaderTest.class.php b/src/test/php/img/unittest/AvifImageReaderTest.class.php
new file mode 100755
index 00000000..42915b0f
--- /dev/null
+++ b/src/test/php/img/unittest/AvifImageReaderTest.class.php
@@ -0,0 +1,16 @@
+<?php namespace img\unittest;
+
+use img\Image;
+use img\io\AvifStreamReader;
+use io\streams\MemoryInputStream;
+use test\Test;
+
+#[ImageTypeSupport('avif')]
+class AvifImageReaderTest {
+  const BYTES= 'AAAAIGZ0eXBhdmlmAAAAAGF2aWZtaWYxbWlhZk1BMUIAAADybWV0YQAAAAAAAAAoaGRscgAAAAAAAAAAcGljdAAAAAAAAAAAAAAAAGxpYmF2aWYAAAAADnBpdG0AAAAAAAEAAAAeaWxvYwAAAABEAAABAAEAAAABAAABGgAAABoAAAAoaWluZgAAAAAAAQAAABppbmZlAgAAAAABAABhdjAxQ29sb3IAAAAAamlwcnAAAABLaXBjbwAAABRpc3BlAAAAAAAAAAEAAAABAAAAEHBpeGkAAAAAAwgICAAAAAxhdjFDgQAMAAAAABNjb2xybmNseAABAA0AAYAAAAAXaXBtYQAAAAAAAAABAAEEAQKDBAAAACJtZGF0EgAKCBgABggIaAwgMgwXgAkkkkQAAHlM1uhudWxsCg==';
+
+  #[Test]
+  public function read() {
+    Image::loadFrom(new AvifStreamReader(new MemoryInputStream(base64_decode(self::BYTES))));
+  }
+}
\ No newline at end of file
diff --git a/src/test/php/img/unittest/AvifImageWriterTest.class.php b/src/test/php/img/unittest/AvifImageWriterTest.class.php
new file mode 100755
index 00000000..f6ac3aec
--- /dev/null
+++ b/src/test/php/img/unittest/AvifImageWriterTest.class.php
@@ -0,0 +1,27 @@
+<?php namespace img\unittest;
+
+use img\ImagingException;
+use img\io\AvifStreamWriter;
+use io\OperationFailed;
+use io\streams\{MemoryOutputStream, OutputStream};
+use test\{Assert, Expect, Test};
+
+#[ImageTypeSupport('avif')]
+class AvifImageWriterTest extends AbstractImageWriterTest {
+
+  #[Test, Expect(ImagingException::class)]
+  public function write_error() {
+    $this->image->saveTo(new AvifStreamWriter(new class() implements OutputStream {
+      public function write($arg) { throw new OperationFailed('Could not write: Intentional exception'); }
+      public function flush() { }
+      public function close() { }
+    }));
+  }
+
+  #[Test]
+  public function write() {
+    $s= new MemoryOutputStream();
+    $this->image->saveTo(new AvifStreamWriter($s));
+    Assert::notEquals('', $s->bytes());
+  }
+}
\ No newline at end of file
diff --git a/src/test/php/img/unittest/ImageTypeSupport.class.php b/src/test/php/img/unittest/ImageTypeSupport.class.php
index 942e5998..00f432c3 100755
--- a/src/test/php/img/unittest/ImageTypeSupport.class.php
+++ b/src/test/php/img/unittest/ImageTypeSupport.class.php
@@ -32,7 +32,7 @@ public function assertions(Context $context) {
     $supported= imagetypes();
     foreach ($this->types as $type) {
       yield new Assertion(
-        $supported & constant('IMG_'.strtoupper($type)),
+        $supported & defined('IMG_'.strtoupper($type)),
         new Verify('Image type "'.$type.'" is supported')
       );
     }