diff --git a/generator/osm_o5m_source.hpp b/generator/osm_o5m_source.hpp
index c1a6f49987..d70e91b502 100644
--- a/generator/osm_o5m_source.hpp
+++ b/generator/osm_o5m_source.hpp
@@ -1,3 +1,4 @@
+// See O5M Format definition at http://wiki.openstreetmap.org/wiki/O5m
 #pragma once
 
 #include "std/algorithm.hpp"