diff --git a/CMakeLists.txt b/CMakeLists.txt
index a2fc66a..dac914c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -501,7 +501,7 @@ else()
         set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
     endif()
     if(NOT CMAKE_BUILD_TYPE)
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O2")
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O3")
     endif()
 endif()