--- a/CMakeLists.txt	2017-03-04 16:40:12.180902990 +1100
+++ b/CMakeLists.txt	2017-03-04 16:39:07.544523347 +1100
@@ -4,7 +4,7 @@
 set(xc3sprog_VERSION_MINOR 0)
 
 SET(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}")
-set(CMAKE_CXX_FLAGS "-g -Wall")
+set(CMAKE_CXX_FLAGS "-g -Wall $ENV{CXXFLAGS}")
 cmake_minimum_required(VERSION 2.6)
 
 find_package(PkgConfig REQUIRED)