diff --git a/CMakeLists.txt b/CMakeLists.txt
index f04b8e63af..abc464a6d4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -149,7 +149,7 @@ if(MSVC)
 endif()
 
 if(UNIX)
-  add_definitions("-std=c++11")
+  set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
 endif()
 
 if(NOT DEFINED LIB_INSTALL_DIR)