Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 26273)
+++ wp-includes/functions.php	(working copy)
@@ -285,6 +285,7 @@
 			// or else fall through
 		case 'a' :
 		case 'O' :
+		case 'C' :
 			return (bool) preg_match( "/^{$token}:[0-9]+:/s", $data );
 		case 'b' :
 		case 'i' :