diff --git a/ng/CMakeLists.txt b/ng/CMakeLists.txt
index db746b7d..34977a86 100644
--- a/ng/CMakeLists.txt
+++ b/ng/CMakeLists.txt
@@ -3,7 +3,7 @@ set(netgen_sources demoview.cpp ngappinit.cpp onetcl.cpp parallelfunc.cpp ngpkg.
 if(USE_GUI)
 
     add_executable(netgen ${netgen_sources})
-    target_link_libraries( netgen nglib ${ZLIB_LIBRARIES} ${LIBTOGL} ${TK_LIBRARY} ${TCL_LIBRARY} ${JPEG_LIBRARIES} ${FFMPEG_LIBRARIES})
+    target_link_libraries( netgen nglib ${ZLIB_LIBRARIES} ${LIBTOGL} ${TK_LIBRARY} ${TCL_LIBRARY} ${JPEG_LIBRARIES} ${FFMPEG_LIBRARIES} ${X11_X11_LIB})
     if(NOT WIN32)
       target_link_libraries( netgen mesh stlvis stl geom2dvis interface geom2d csg stl visual csgvis )
     endif(NOT WIN32)