Index: erts/lib_src/Makefile.in
--- erts/lib_src/Makefile.in.orig
+++ erts/lib_src/Makefile.in
@@ -43,7 +43,7 @@ INSTALL_PROGRAM=@INSTALL_PROGRAM@
 ERLANG_OSTYPE=@ERLANG_OSTYPE@
 
 OMIT_FP=false
-CFLAGS=$(subst O2,O3, @CFLAGS@)
+CFLAGS=@CFLAGS@
 LDFLAGS=@LDFLAGS@
 
 ifeq ($(TYPE),debug)
