--- flightgear-3.4.0/utils/fgviewer/CMakeLists.txt.orig	2015-03-21 16:09:22.409159138 +0100
+++ flightgear-3.4.0/utils/fgviewer/CMakeLists.txt	2015-03-21 16:09:34.839172400 +0100
@@ -48,5 +48,6 @@
 	${OPENGL_LIBRARIES}
 	${FGVIEWER_RTI_LIBRARIES}
         ${SIMGEAR_CORE_LIBRARY_DEPENDENCIES}
+        -lX11
 )
 install(TARGETS fgviewer RUNTIME DESTINATION bin)