diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1c0f705..7b83ee7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -351,7 +351,7 @@ elseif (CMAKE_BUILD_TYPE STREQUAL "Release")
     else()
       string(REPLACE "-O2" "" CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}")
       string(REPLACE "-O3" "" CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}")
-      set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -Ofast")
+      set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -O3")
     endif()
     if (NOT MSVC)
       set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -s")
@@ -368,7 +368,7 @@ elseif (CMAKE_BUILD_TYPE STREQUAL "RelWithDebInfo")
       string(REPLACE "-O2" "" CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO}")
       string(REPLACE "-O3" "" CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO}")
       if (NOT ENABLE_SYSTEM_GMIC)
-          set_source_files_properties(${GMIC_PATH}/gmic.cpp PROPERTIES COMPILE_FLAGS "-Ofast")
+          set_source_files_properties(${GMIC_PATH}/gmic.cpp PROPERTIES COMPILE_FLAGS "-O3")
       endif (NOT ENABLE_SYSTEM_GMIC)
       set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO} -O2")
     endif()