Jetpack content_width Gallery Issue

I have an issue with Jetpack setting the Gallery width at 500 px while I need 640 px for my theme.

In Jetpack’s tilled-gallery.php I see:

if ( ! $tiled_gallery_content_width )
			$tiled_gallery_content_width = 500;

In WooThemes Canvas, the theme I am using, it’s set like this:

// Set the content width based on the theme's design and stylesheet.
		if ( ! isset( $content_width ) ) {
			$content_width = 640;
		}

But the with is still on 500 px. See the gallery used at http://melodiefabriek.com/blog/exhibitions-anton-corbijn/

How can I fix this?