Index: wp-includes/class-wp-theme.php
===================================================================
--- wp-includes/class-wp-theme.php	(revision 26859)
+++ wp-includes/class-wp-theme.php	(working copy)
@@ -673,7 +673,7 @@
 					/* translators: used between list items, there is a space after the comma */
 					$comma = __( ', ' );
 				}
-				$value = implode( $comma, $value );
+				$value = implode( $comma, (array) $value );
 				break;
 			case 'ThemeURI' :
 			case 'AuthorURI' :