Index: src/wp-includes/formatting.php
===================================================================
--- src/wp-includes/formatting.php	(revision 55614)
+++ src/wp-includes/formatting.php	(working copy)
@@ -4859,7 +4859,9 @@
 			break;
 
 		case 'gmt_offset':
-			$value = preg_replace( '/[^0-9:.-]/', '', $value ); // Strips slashes.
+			if ( is_string( $value ) ) {
+				$value = preg_replace( '/[^0-9:.-]/', '', $value ); // Strips slashes.
+			}
 			break;
 
 		case 'siteurl':