diff --git a/wp-blog-header.php b/wp-blog-header.php
index 23f12c559f..c700942cce 100644
--- a/wp-blog-header.php
+++ b/wp-blog-header.php
@@ -92,7 +92,7 @@ if (!isset($doing_rss) || !$doing_rss) {
 	// We're showing a feed, so WP is indeed the only thing that last changed
 	$wp_last_modified = mysql2date('D, d M Y H:i:s', get_lastpostmodified('GMT'), 0).' GMT';
 	$wp_etag = '"'.md5($wp_last_modified).'"';
-	@header('Last Modified: '.$wp_last_modified);
+	@header('Last-Modified: '.$wp_last_modified);
 	@header('ETag: '.$wp_etag);
 	@header ('X-Pingback: ' . get_settings('siteurl') . '/xmlrpc.php');