diff --git a/src/wp-includes/media.php b/src/wp-includes/media.php
index 804a34f6ac..389be76f29 100644
--- a/src/wp-includes/media.php
+++ b/src/wp-includes/media.php
@@ -1023,7 +1023,8 @@ function wp_get_attachment_image_src( $attachment_id, $size = 'thumbnail', $icon
  *                                  will result in the attribute being omitted for the image.
  *                                  Defaults to 'lazy', depending on wp_lazy_loading_enabled().
  *     @type string       $decoding The 'decoding' attribute value. Possible values are
- *                                  'async' (default), 'sync', or 'auto'.
+ *                                  'async' (default), 'sync', or 'auto'. Passing false or an empty
+ *                                  string will result in the attribute being omitted.
  * }
  * @return string HTML img element or empty string on failure.
  */
@@ -1056,6 +1057,11 @@ function wp_get_attachment_image( $attachment_id, $size = 'thumbnail', $icon = f
 
 		$attr = wp_parse_args( $attr, $default_attr );
 
+		// Omit the `decoding` attribute if the value is invalid according to the spec.
+		if ( empty( $attr['decoding'] ) || ! in_array( $attr['decoding'], array( 'async', 'sync', 'auto' ), true ) ) {
+			unset( $attr['decoding'] );
+		}
+
 		// If the default value of `lazy` for the `loading` attribute is overridden
 		// to omit the attribute for this image, ensure it is not included.
 		if ( array_key_exists( 'loading', $attr ) && ! $attr['loading'] ) {
diff --git a/tests/phpunit/tests/media.php b/tests/phpunit/tests/media.php
index 5165e32b85..994b4b7c72 100644
--- a/tests/phpunit/tests/media.php
+++ b/tests/phpunit/tests/media.php
@@ -3278,6 +3278,81 @@ EOF;
 		$this->assertStringNotContainsString( ' loading=', $img );
 	}
 
+	/**
+	 * @ticket 57086
+	 *
+	 * @dataProvider data_wp_get_attachment_image_decoding_attr
+	 *
+	 * @covers ::wp_get_attachment_image
+	 */
+	public function test_wp_get_attachment_image_decoding_attr( $decoding, $expected ) {
+		if ( 'no value' === $decoding ) {
+			$image = wp_get_attachment_image( self::$large_id, 'thumbnail', false, array() );
+		} else {
+			$image = wp_get_attachment_image( self::$large_id, 'thumbnail', false, array( 'decoding' => $decoding ) );
+		}
+
+		if ( 'no value' === $expected ) {
+			$this->assertStringNotContainsString( ' decoding=', $image );
+		} else {
+			$this->assertStringContainsString( ' decoding="' . esc_attr( $expected ) . '"', $image );
+		}
+	}
+
+	/**
+	 * Data provider for test_wp_get_attachment_image_decoding_attr().
+	 *
+	 * @return array[]
+	 */
+	public function data_wp_get_attachment_image_decoding_attr() {
+		return array(
+			'default'     => array(
+				'decoding' => 'no value',
+				'expected' => 'async',
+			),
+			'async'       => array(
+				'decoding' => 'async',
+				'expected' => 'async',
+			),
+			'sync'        => array(
+				'decoding' => 'sync',
+				'expected' => 'sync',
+			),
+			'auto'        => array(
+				'decoding' => 'auto',
+				'expected' => 'auto',
+			),
+			'empty'       => array(
+				'decoding' => '',
+				'expected' => 'no value',
+			),
+			'false'       => array(
+				'decoding' => false,
+				'expected' => 'no value',
+			),
+			'null'        => array(
+				'decoding' => null,
+				'expected' => 'no value',
+			),
+			'zero'        => array(
+				'decoding' => 0,
+				'expected' => 'no value',
+			),
+			'zero string' => array(
+				'decoding' => '0',
+				'expected' => 'no value',
+			),
+			'zero float'  => array(
+				'decoding' => 0.0,
+				'expected' => 'no value',
+			),
+			'invalid'     => array(
+				'decoding' => 'invalid',
+				'expected' => 'no value',
+			),
+		);
+	}
+
 	/**
 	 * @ticket 44427
 	 * @ticket 50425