diff --git a/src/wp-includes/blocks.php b/src/wp-includes/blocks.php
index 6fc72e358a..590f3706f7 100644
--- a/src/wp-includes/blocks.php
+++ b/src/wp-includes/blocks.php
@@ -794,16 +794,22 @@ function get_comment_delimited_block_content( $block_name, $block_attributes, $b
  * instead preserve the markup as parsed.
  *
  * @since 5.3.1
+ * @since 6.4.0 The `$callback` parameter was added.
  *
- * @param array $block A representative array of a single parsed block object. See WP_Block_Parser_Block.
+ * @param array         $block    A representative array of a single parsed block object. See WP_Block_Parser_Block.
+ * @param callable|null $callback Optional. Callback to run on each block in the tree before serialization. Default null.
  * @return string String of rendered HTML.
  */
-function serialize_block( $block ) {
+function serialize_block( $block, $callback = null ) {
+	if ( is_callable( $callback ) ) {
+		$block = call_user_func( $callback, $block );
+	}
+
 	$block_content = '';
 
 	$index = 0;
 	foreach ( $block['innerContent'] as $chunk ) {
-		$block_content .= is_string( $chunk ) ? $chunk : serialize_block( $block['innerBlocks'][ $index++ ] );
+		$block_content .= is_string( $chunk ) ? $chunk : serialize_block( $block['innerBlocks'][ $index++ ], $callback );
 	}
 
 	if ( ! is_array( $block['attrs'] ) ) {
@@ -822,12 +828,18 @@ function serialize_block( $block ) {
  * parsed blocks.
  *
  * @since 5.3.1
+ * @since 6.4.0 The `$callback` parameter was added.
  *
- * @param array[] $blocks An array of representative arrays of parsed block objects. See serialize_block().
+ * @param array[]       $blocks   An array of representative arrays of parsed block objects. See serialize_block().
+ * @param callable|null $callback Optional. Callback to run on each block in the tree before serialization. Default null.
  * @return string String of rendered HTML.
  */
-function serialize_blocks( $blocks ) {
-	return implode( '', array_map( 'serialize_block', $blocks ) );
+function serialize_blocks( $blocks, $callback = null ) {
+	$result = '';
+	foreach ( $blocks as $block ) {
+		$result .= serialize_block( $block, $callback );
+	};
+	return $result;
 }
 
 /**
diff --git a/tests/phpunit/tests/blocks/serialize.php b/tests/phpunit/tests/blocks/serialize.php
index 4437c8ca85..3bfda3ed55 100644
--- a/tests/phpunit/tests/blocks/serialize.php
+++ b/tests/phpunit/tests/blocks/serialize.php
@@ -54,4 +54,28 @@ class Tests_Blocks_Serialize extends WP_UnitTestCase {
 		$this->assertSame( 'example', strip_core_block_namespace( 'core/example' ) );
 		$this->assertSame( 'plugin/example', strip_core_block_namespace( 'plugin/example' ) );
 	}
+
+	/**
+	 * @ticket 59327
+	 *
+	 * @covers ::serialize_blocks
+	 */
+	public function test_callback_argument() {
+		$markup = "<!-- wp:outer --><!-- wp:inner {\"key\":\"value\"} -->Example.<!-- /wp:inner -->\n\nExample.\n\n<!-- wp:void /--><!-- /wp:outer -->";
+		$blocks = parse_blocks( $markup );
+
+		$actual = serialize_blocks( $blocks, array( __CLASS__, 'add_attribute_to_inner_block' ) );
+
+		$this->assertSame(
+			"<!-- wp:outer --><!-- wp:inner {\"key\":\"value\",\"myattr\":\"myvalue\"} -->Example.<!-- /wp:inner -->\n\nExample.\n\n<!-- wp:void /--><!-- /wp:outer -->",
+			$actual
+		);
+	}
+
+	public static function add_attribute_to_inner_block( $block ) {
+		if ( 'core/inner' === $block['blockName'] ) {
+			$block['attrs']['myattr'] = 'myvalue';
+		}
+		return $block;
+	}
 }