diff --git a/include/GammaLib.hpp b/include/GammaLib.hpp
index 36fb4dc..80cf923 100644
--- a/include/GammaLib.hpp
+++ b/include/GammaLib.hpp
@@ -136,6 +136,7 @@
 
 /* __ Skymap handling ____________________________________________________ */
 #include "GSkyDir.hpp"
+#include "GHorizDir.hpp"
 #include "GSkyPixel.hpp"
 #include "GSkymap.hpp"
 #include "GSkyRegions.hpp"