diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index e6ed5be376..3702647f9d 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -79,6 +79,7 @@ if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CXX_FLAGS)
   #release comes with -O3 by default
   set(CMAKE_BUILD_TYPE Release CACHE STRING "Choose the type of build, options are: None Debug Release RelWithDebInfo MinSizeRel." FORCE)
 endif(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CXX_FLAGS)
+string(TOUPPER "${CMAKE_BUILD_TYPE}" BTYPE)
 
 # check for files auto-generated by make-based buildsystem
 # this is fast, so check for it all the time
@@ -444,10 +445,12 @@ if(PKG_VORONOI)
     include(ExternalProject)
 
     if(BUILD_SHARED_LIBS)
-      set(VORO_BUILD_OPTIONS CXX="${CMAKE_CXX_COMPILER}" CFLAGS="${CMAKE_SHARED_LIBRARY_CXX_FLAGS} ${CMAKE_CXX_FLAGS}")
+      set(VORO_BUILD_CFLAGS "${CMAKE_SHARED_LIBRARY_CXX_FLAGS} ${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${BTYPE}}")
     else()
-      set(VORO_BUILD_OPTIONS CXX="${CMAKE_CXX_COMPILER}" CFLAGS="${CMAKE_CXX_FLAGS}")
+      set(VORO_BUILD_CFLAGS "${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${BTYPE}}")
     endif()
+    string(APPEND VORO_BUILD_CFLAGS ${CMAKE_CXX_FLAGS})
+    set(VORO_BUILD_OPTIONS CXX=${CMAKE_CXX_COMPILER} CFLAGS=${VORO_BUILD_CFLAGS})
 
     ExternalProject_Add(voro_build
       URL http://math.lbl.gov/voro++/download/dir/voro++-0.4.6.tar.gz
@@ -1455,7 +1458,6 @@ foreach(PKG ${DEFAULT_PACKAGES} ${ACCEL_PACKAGES} ${OTHER_PACKAGES})
   endif()
 endforeach()
 
-string(TOUPPER "${CMAKE_BUILD_TYPE}" BTYPE)
 get_directory_property(CPPFLAGS DIRECTORY ${CMAKE_SOURCE_DIR} COMPILE_DEFINITIONS)
 include(FeatureSummary)
 feature_summary(DESCRIPTION "The following packages have been found:" WHAT PACKAGES_FOUND)