--- a/configure.ac
+++ b/configure.ac
@@ -65,7 +65,7 @@ if test "$debug" = "yes"; then
 else
   AC_SUBST( debug, [no] )
   AC_SUBST( cppflag, [] )
-  AC_SUBST( cxxflag, [-O3] )
+  AC_SUBST( cxxflag, [] )
   AC_SUBST( object_path, [Release] )
 fi
 AC_MSG_RESULT($debug)