diff --git a/cmake/modules/BuildBoost.cmake b/cmake/modules/BuildBoost.cmake
index ba86ecaa63..b969c42911 100644
--- a/cmake/modules/BuildBoost.cmake
+++ b/cmake/modules/BuildBoost.cmake
@@ -62,7 +62,7 @@ function(do_build_boost version)
   else()
     list(APPEND boost_features "address-model=32")
   endif()
-  set(BOOST_CXXFLAGS "-fPIC -w") # check on arm, etc <---XXX
+  set(BOOST_CXXFLAGS "${CMAKE_CXX_FLAGS} -fPIC -w") # check on arm, etc <---XXX
   list(APPEND boost_features "cxxflags=${BOOST_CXXFLAGS}")
 
   set(boost_with_libs)