diff --git a/mu-plugins/blocks/local-navigation-bar/index.php b/mu-plugins/blocks/local-navigation-bar/index.php
index 804188aa2..33787058d 100644
--- a/mu-plugins/blocks/local-navigation-bar/index.php
+++ b/mu-plugins/blocks/local-navigation-bar/index.php
@@ -10,6 +10,7 @@
 
 add_action( 'init', __NAMESPACE__ . '\init' );
 add_filter( 'render_block_data', __NAMESPACE__ . '\update_block_attributes' );
+add_filter( 'render_block', __NAMESPACE__ . '\customize_navigation_block_icon', 10, 2 );
 
 /**
  * Registers the block using the metadata loaded from the `block.json` file.
@@ -91,3 +92,51 @@ function update_block_attributes( $block ) {
 
 	return $block;
 }
+
+/**
+ * Replace a nested navigation block mobile button icon with a caret icon.
+ * Only applies if it has the 3 bar icon set, as this has an svg with <path> to update. 
+ *
+ * @param string $block_content The block content.
+ * @param array  $block The parsed block data.
+ *
+ * @return string
+ */
+function customize_navigation_block_icon( $block_content, $block ) {
+	return $block_content;
+
+	if ( ! empty( $block['blockName'] ) && 'wporg/local-navigation-bar' === $block['blockName'] ) {
+		$tag_processor = new \WP_HTML_Tag_Processor( $block_content );
+
+		if (
+			$tag_processor->next_tag( array( 
+				'tag_name' => 'nav', 
+				'class_name' => 'wp-block-navigation' 
+			)
+		) ) {
+			if ( 
+				$tag_processor->next_tag( array( 
+					'tag_name' => 'button', 
+					'class_name' => 'wp-block-navigation__responsive-container-open' 
+				) ) &&
+				$tag_processor->next_tag( 'path' )
+			) {
+				$tag_processor->set_attribute( 'd', 'M17.5 11.6L12 16l-5.5-4.4.9-1.2L12 14l4.5-3.6 1 1.2z' );
+			}
+		
+			if ( 
+				$tag_processor->next_tag( array( 
+					'tag_name' => 'button', 
+					'class_name' => 'wp-block-navigation__responsive-container-close' 
+				) ) &&
+				$tag_processor->next_tag( 'path' )
+			) {
+				$tag_processor->set_attribute( 'd', 'M6.5 12.4L12 8l5.5 4.4-.9 1.2L12 10l-4.5 3.6-1-1.2z' );
+			}
+		
+			return $tag_processor->get_updated_html();
+		}
+	}
+
+	return $block_content;
+}