diff --git a/wp-content/themes/twentyten/header.php b/wp-content/themes/twentyten/header.php
index 2c44e8d01..54971c930 100644
--- a/wp-content/themes/twentyten/header.php
+++ b/wp-content/themes/twentyten/header.php
@@ -67,7 +67,7 @@
 
 				<?php
 					// Check if this is a post or page, if it has a thumbnail, and if it's a big one
-					if ( is_singular() &&
+					if ( is_singular() && current_theme_supports( 'post-thumbnails' ) &&
 							has_post_thumbnail( $post->ID ) &&
 							( /* $src, $width, $height */ $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'post-thumbnail' ) ) &&
 							$image[1] >= HEADER_IMAGE_WIDTH ) :