diff --git a/src/wp-includes/class-wp-block-parser.php b/src/wp-includes/class-wp-block-parser.php
index 81cb7a8fa21f7..6c1eb715a7ac1 100644
--- a/src/wp-includes/class-wp-block-parser.php
+++ b/src/wp-includes/class-wp-block-parser.php
@@ -342,7 +342,7 @@ public function add_freeform( $length = null ) {
 	 * @param int|null              $last_offset  Last byte offset into document if continuing form earlier output.
 	 */
 	public function add_inner_block( WP_Block_Parser_Block $block, $token_start, $token_length, $last_offset = null ) {
-		$parent                       = $this->stack[ array_key_last( $this->stack ) ];
+		$parent                       = array_last( $this->stack );
 		$parent->block->innerBlocks[] = (array) $block;
 		$html                         = substr( $this->document, $parent->prev_offset, $token_start - $parent->prev_offset );