diff --git a/wp-includes/category-template.php b/wp-includes/category-template.php
index 3c7d10e215..385567babe 100644
--- a/wp-includes/category-template.php
+++ b/wp-includes/category-template.php
@@ -238,7 +238,10 @@ function wp_list_categories($args = '') {
 			$output .= __("No categories");
 	} else {
 		global $wp_query;
-		$r['current_category'] = $wp_query->get_queried_object_id();
+		
+		if ( is_category() )
+			$r['current_category'] = $wp_query->get_queried_object_id();
+
 		if ( $hierarchical )
 			$depth = 0;  // Walk the full depth.
 		else
diff --git a/wp-includes/classes.php b/wp-includes/classes.php
index 5ae587cb7f..b9713af0d9 100644
--- a/wp-includes/classes.php
+++ b/wp-includes/classes.php
@@ -619,13 +619,14 @@ class Walker_Category extends Walker {
 			$link .= ' ' . gmdate('Y-m-d', $category->last_update_timestamp);
 		}
 
-		$_current_category = get_category( $current_category );
+		if ( $current_category )
+			$_current_category = get_category( $current_category );
 
 		if ( 'list' == $args['style'] ) {
 			$output .= "\t<li";
-			if ( ($category->cat_ID == $current_category) && is_category() )
+			if ( $current_category && ($category->cat_ID == $current_category) )
 				$output .=  ' class="current-cat"';
-			elseif ( ($category->cat_ID == $_current_category->category_parent) && is_category() )
+			elseif ( $_current_category && ($category->cat_ID == $_current_category->category_parent) )
 				$output .=  ' class="current-cat-parent"';
 			$output .= ">$link\n";
 		} else {