Index: wp-content/themes/twentythirteen/functions.php
===================================================================
--- wp-content/themes/twentythirteen/functions.php	(revision 24432)
+++ wp-content/themes/twentythirteen/functions.php	(working copy)
@@ -580,3 +580,18 @@
 	wp_enqueue_script( 'twentythirteen-customizer', get_template_directory_uri() . '/js/theme-customizer.js', array( 'customize-preview' ), '20130226', true );
 }
 add_action( 'customize_preview_init', 'twentythirteen_customize_preview_js' );
+
+/**
+ * Get the medium image instead of the small one when embedding from Instagram
+ *
+ * @since Twenty Thirteen 1.0
+ */
+function twentythirteen_oembed_fetch_url( $provider, $url, $args ) {
+	if ( 0 !== strpos( $provider, 'http://api.instagram.com/oembed' ) && $args['width'] < 612 )
+		return $provider;
+
+	return add_query_arg( 'maxwidth', 612, $provider );
+}
+add_filter( 'oembed_fetch_url', 'twentythirteen_oembed_fetch_url', 10, 3 );
+
+