Correctly import image caption as caption than description in WordPress

gistfile1.php

<?php

function add_attachment_caption( $meta, $attachment_id ) {
	if ( ! empty( $meta['image_meta']['caption'] ) ) {
		$data					= array(
			'ID'				=> $attachment_id,
			// remove wrongly imported caption as description field
			'post_content'		=> '',
			'post_excerpt'		=> $meta['image_meta']['caption'],
		);

		wp_update_post( $data );
	}

	return $meta;
}

add_filter('wp_generate_attachment_metadata', 'add_attachment_caption', '', 2);

?>