Index: src/modules/userinterface/legacymenu/CMakeLists.txt
--- src/modules/userinterface/legacymenu/CMakeLists.txt.orig
+++ src/modules/userinterface/legacymenu/CMakeLists.txt
@@ -78,6 +78,10 @@ ADD_SDL2_INCLUDEDIR()
 
 ADD_ENET_INCLUDEDIR()
 
+IF(UNIX)
+    INCLUDE_DIRECTORIES(${X11_INCLUDE_DIR})
+ENDIF(UNIX)
+
 IF(WIN32)
     # DLL export stuff under Windows (to avoid .def file)
     ADD_DEFINITIONS(-DLEGACYMENU_DLL)
