Index: wp-content/themes/twentyeleven/header.php
===================================================================
--- wp-content/themes/twentyeleven/header.php	(revision 20948)
+++ wp-content/themes/twentyeleven/header.php	(working copy)
@@ -79,7 +79,12 @@
 				// Check to see if the header image has been removed
 				$header_image = get_header_image();
 				if ( $header_image ) :
-					$header_image_width  = get_custom_header()->width;
+					if ( function_exists( 'get_custom_header' ) ) {
+						$header_image_width  = get_custom_header()->width;
+						$header_image_height = get_custom_header()->height;
+					} else {
+						$header_image_height = $header_image_width = '';
+					}
 			?>
 			<a href="<?php echo esc_url( home_url( '/' ) ); ?>">
 				<?php
@@ -91,7 +96,7 @@
 						// Houston, we have a new header image!
 						echo get_the_post_thumbnail( $post->ID, 'post-thumbnail' );
 					else : ?>
-					<img src="<?php header_image(); ?>" width="<?php echo $header_image_width; ?>" height="<?php echo get_custom_header()->height; ?>" alt="" />
+					<img src="<?php header_image(); ?>" width="<?php echo $header_image_width; ?>" height="<?php echo $header_image_height; ?>" alt="" />
 				<?php endif; // end check for featured image or standard header ?>
 			</a>
 			<?php endif; // end check for removed header image ?>