--- base/configure.ac.orig	2010-08-01 22:37:05.000000000 +0900
+++ base/configure.ac	2010-08-01 22:41:12.000000000 +0900
@@ -402,7 +402,7 @@
 	PNGDEVS="$PNGDEVS_ALL"
 else
 	AC_MSG_RESULT([no])
-	AC_CHECK_LIB(png, png_check_sig, [
+	AC_CHECK_LIB(png, png_sig_cmp, [
 	  AC_CHECK_HEADERS(png.h, [
 		SHARE_LIBPNG=1
 		PNGDEVS="$PNGDEVS_ALL"
@@ -434,7 +434,7 @@
 	AC_CHECK_LIB(tiff, TIFFOpen,
 		     [AC_CHECK_HEADERS(tiff.h, [HAVE_SYSTEM_LIBTIFF=1;SHARE_LIBTIFF=1])],
 		     [], [-ljpeg])
-	if test -z $LOCAL_LIBTIFF_VERSION && test "x$HAVE_SYSTEM_LIBTIFF" == x; then
+	if test -z $LOCAL_LIBTIFF_VERSION && test "x$HAVE_SYSTEM_LIBTIFF" = x; then
 	    AC_MSG_NOTICE([Could not find a copy of libtiff on your system.
 Disabling tiff output devices.])
 	else