diff --git a/src/wp-includes/blocks.php b/src/wp-includes/blocks.php
index bef4ea3bce6e8..59888736f7c5d 100644
--- a/src/wp-includes/blocks.php
+++ b/src/wp-includes/blocks.php
@@ -853,18 +853,24 @@ function get_comment_delimited_block_content( $block_name, $block_attributes, $b
  *
  * @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.
+ *                                It is called with the following arguments: $block, $parent_block, $block_index, $chunk_index.
  * @return string String of rendered HTML.
  */
 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++ ], $callback );
+	$block_index = 0;
+	foreach ( $block['innerContent'] as $chunk_index => $chunk ) {
+		if ( is_string( $chunk ) ) {
+			$block_content .= $chunk;
+		} else {
+			$inner_block = $block['innerBlocks'][ $block_index ];
+			if ( is_callable( $callback ) ) {
+				$inner_block = call_user_func( $callback, $inner_block, $block, $block_index, $chunk_index );
+			}
+			$block_index++;
+			$block_content .= serialize_block( $inner_block, $callback );
+		}
 	}
 
 	if ( ! is_array( $block['attrs'] ) ) {
@@ -887,11 +893,16 @@ function serialize_block( $block, $callback = null ) {
  *
  * @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.
+ *                                It is called with the following arguments: $block, $parent_block, $block_index, $chunk_index.
  * @return string String of rendered HTML.
  */
 function serialize_blocks( $blocks, $callback = null ) {
 	$result = '';
 	foreach ( $blocks as $block ) {
+		if ( is_callable( $callback ) ) {
+			// At the top level, there is no parent block, block index, or chunk index to pass to the callback.
+			$block = call_user_func( $callback, $block );
+		}
 		$result .= serialize_block( $block, $callback );
 	}
 	return $result;