diff --git a/CMakeLists.txt b/CMakeLists.txt
index 337fd19a4..10b4bf17c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -132,6 +132,7 @@ else()
     if(Boost_TIMER_LIBRARY)
       list(APPEND GTSAM_BOOST_LIBRARIES ${Boost_TIMER_LIBRARY} ${Boost_CHRONO_LIBRARY})
     else()
+      list(APPEND GTSAM_BOOST_LIBRARIES rt) # When using the header-only boost timer library, need -lrt
       message("WARNING:  GTSAM timing instrumentation will use the older, less accurate, Boost timer library because boost older than 1.48 was found.")
     endif()
 endif()