Index: src/modules/graphic/ssggraph/CMakeLists.txt
--- src/modules/graphic/ssggraph/CMakeLists.txt.orig
+++ src/modules/graphic/ssggraph/CMakeLists.txt
@@ -48,6 +48,10 @@ IF(COMMAND CMAKE_POLICY)
     CMAKE_POLICY(SET CMP0003 NEW)
 ENDIF(COMMAND CMAKE_POLICY)
 
+IF(UNIX)
+    INCLUDE_DIRECTORIES(${X11_INCLUDE_DIR})
+ENDIF(UNIX)
+
 IF(WIN32)
     # DLL export stuff under Windows (to avoid .def file)
     ADD_DEFINITIONS(-DSSGGRAPH_DLL)
