diff --git a/vlib/v/doc/doc.v b/vlib/v/doc/doc.v
index c6d601a114..801e0e9f71 100644
--- a/vlib/v/doc/doc.v
+++ b/vlib/v/doc/doc.v
@@ -144,6 +144,7 @@ pub fn (nodes []DocNode) find_children_of(parent_type string) []DocNode {
 }
 
 fn get_parent_mod(dir string) ?string {
+	if dir.len == 0  { return error('root folder reached') }
 	base_dir := os.base_dir(dir)
 	if os.file_name(base_dir) in ['encoding', 'v'] && 'vlib' in base_dir {
 		return os.file_name(base_dir)