diff --git a/rclcpp/CMakeLists.txt b/rclcpp/CMakeLists.txt
index 849031c..7a7a8e9 100644
--- a/rclcpp/CMakeLists.txt
+++ b/rclcpp/CMakeLists.txt
@@ -13,7 +13,7 @@ find_package(rosidl_typesupport_c REQUIRED)
 find_package(rosidl_typesupport_cpp REQUIRED)
 
 if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-  set(CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS} "-std=c++14")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
   add_compile_options(-Wall -Wextra -Wpedantic)
 endif()
 
diff --git a/rclcpp_lifecycle/CMakeLists.txt b/rclcpp_lifecycle/CMakeLists.txt
index 2da6eb1..c013416 100644
--- a/rclcpp_lifecycle/CMakeLists.txt
+++ b/rclcpp_lifecycle/CMakeLists.txt
@@ -3,7 +3,7 @@ cmake_minimum_required(VERSION 3.5)
 project(rclcpp_lifecycle)
 
 if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-  set(CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS} "-std=c++14")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
   add_compile_options(-Wall -Wextra -Wpedantic)
 endif()