--- CMakeLists.txt
+++ CMakeLists.txt
@@ -10,5 +10,5 @@
 
 # Compile options
-set (CMAKE_CXX_FLAGS "-std=c++11 -Wall -Weffc++ -Wshadow -Wconversion")
+set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Wall -Weffc++ -Wshadow -Wconversion")
 
 IF(NOT CMAKE_BUILD_TYPE)
