Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 17856)
+++ wp-includes/functions.php	(working copy)
@@ -265,6 +265,7 @@
 			if ( '"' !== $data[$length-2] )
 				return false;
 		case 'a' :
+		case 'C' :
 		case 'O' :
 			return (bool) preg_match( "/^{$token}:[0-9]+:/s", $data );
 		case 'b' :