diff --git a/config/optimize b/config/optimize
index 4f47ba12d..6786d9bae 100644
--- a/config/optimize
+++ b/config/optimize
@@ -34,10 +34,10 @@ LDFLAGS_OPTIM_LINKER_GOLD="-fuse-ld=gold"
 LDFLAGS_OPTIM_LINKER_MOLD="-fuse-ld=mold"
 
 # default compiler optimization
-CFLAGS_OPTIM_DEFAULT="-O3 -fomit-frame-pointer -DNDEBUG"
+CFLAGS_OPTIM_DEFAULT="-Ofast -fomit-frame-pointer -DNDEBUG"
 CXXFLAGS_OPTIM_DEFAULT="${CFLAGS_OPTIM_DEFAULT}"
 # speed flag
-CFLAGS_OPTIM_SPEED="-O3 -fomit-frame-pointer -DNDEBUG"
+CFLAGS_OPTIM_SPEED="-Ofast -fomit-frame-pointer -DNDEBUG"
 CXXFLAGS_OPTIM_SPEED="${CFLAGS_OPTIM_SPEED}"
 # size flag
 CFLAGS_OPTIM_SIZE="-Os -fomit-frame-pointer -DNDEBUG"