Index: src/wp-includes/date.php
===================================================================
--- src/wp-includes/date.php	(revision 33000)
+++ src/wp-includes/date.php	(working copy)
@@ -356,9 +356,7 @@
 		// Weeks per year.
 		if ( isset( $_year ) ) {
 			// If we have a specific year, use it to calculate number of weeks.
-			$date = new DateTime();
-			$date->setISODate( $_year, 53 );
-			$week_count = $date->format( "W" ) === "53" ? 53 : 52;
+			$week_count = date('W',mktime(0,0,0,12,28,$date_query['year']));
 
 		} else {
 			// Otherwise set the week-count to a maximum of 53.