--- configure.ac
+++ configure.ac
@@ -77,8 +77,8 @@ AH_TOP([
 AH_BOTTOM([
 /* make sure that we pickup the correct stuff from all headers */
 #ifdef HAVE_FEATURES_H
-#undef _XOPEN_SOURCE /* keep unmodified */
-#undef _BSD_SOURCE /* keep unmodified */
+/* keep unmodified */ #undef _XOPEN_SOURCE
+/* keep unmodified */ #undef _BSD_SOURCE
 #define _XOPEN_SOURCE 600
 #define _BSD_SOURCE 1
 # include <features.h>
@@ -247,14 +247,14 @@ char *strchr (), *strrchr ();
 #if (! defined(HAVE_ISINF) && defined(HAVE_FPCLASS))
 #  define HAVE_ISINF 1
 #  ifdef isinf
-#  undef isinf /* confuse autoconf */
+/* confuse autoconf */ #  undef isinf
 #  endif
 #  define isinf(a) (fpclass(a) == FP_NINF || fpclass(a) == FP_PINF)
 #endif
 
 /* solaris 10 it defines isnan such that only forte can compile it ... bad bad  */
 #if (defined(HAVE_ISNAN) && defined(isnan) && defined(HAVE_FPCLASS))
-#  undef isnan /* confuse autoconf to NOT remove this */
+/* confuse autoconf to NOT remove this */ #  undef isnan
 #  define isnan(a) (fpclass(a) == FP_SNAN || fpclass(a) == FP_QNAN)
 #endif
 
@@ -358,6 +358,7 @@ dnl Check for the compiler and static/sh
 AC_PROG_CC
 AC_PROG_CPP
 AC_PROG_LIBTOOL
+m4_ifdef([LT_OUTPUT],[LT_OUTPUT])
 
 dnl Try to detect/use GNU features
 CFLAGS="$CFLAGS -D_GNU_SOURCE"