diff --git a/cmake/build/core.cmake b/cmake/build/core.cmake
index cfbf7723..957f56ea 100644
--- a/cmake/build/core.cmake
+++ b/cmake/build/core.cmake
@@ -18,7 +18,7 @@ endif()
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wextra")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O3")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O2")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pedantic")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pedantic-errors")
 set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -DDEBUG")