--- a/sim/CMakeLists.txt
+++ b/sim/CMakeLists.txt
@@ -177,7 +177,7 @@ IF(SIM_ENABLE_FPIE)
 ENDIF(SIM_ENABLE_FPIE)
 
 # only needs simlib
-TARGET_LINK_LIBRARIES(sim simlib ${QT_QTMAIN_LIBRARY})
+TARGET_LINK_LIBRARIES(sim simlib ${QT_QTMAIN_LIBRARY} ${X11_X11_LIB})
 
 # set correct install path
 INSTALL(TARGETS sim RUNTIME DESTINATION ${BINDIR})
