diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index 9d2f905af6..46c1cf1740 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -1754,6 +1754,9 @@ function add_theme_support( $feature ) {
 		$_wp_theme_features[$feature] = true;
 	else
 		$_wp_theme_features[$feature] = array_slice( func_get_args(), 1 );
+		
+	if ( $feature == 'post-formats' && is_array( $_wp_theme_features[$feature][0] ) )
+		$_wp_theme_features[$feature][0] = array_intersect( $_wp_theme_features[$feature][0], array_keys( get_post_format_slugs() ) );
 }
 
 /**