diff --git a/configure.in b/configure.in
index aba9d82..b4a27e9 100644
--- a/configure.in
+++ b/configure.in
@@ -64,6 +64,7 @@ AC_PROG_LN_S
 AC_LIBTOOL_WIN32_DLL
 AM_PROG_LIBTOOL
 AC_PROG_MAKE_SET
+PKG_PROG_PKG_CONFIG
 
 dnl ==========================================================================
 
@@ -246,12 +247,30 @@ AC_ARG_WITH(expat,             [  --with-expat=DIR              Use Expat in DIR
 AC_ARG_WITH(expat-includes,    [  --with-expat-includes=DIR     Use Expat includes in DIR], expat_includes=$withval, expat_includes=yes)
 AC_ARG_WITH(expat-lib,         [  --with-expat-lib=DIR          Use Expat library in DIR], expat_lib=$withval, expat_lib=yes)
 
+# if none of expat,expat-includes,expat-libs are specified,
+# pkg-config is referred.
+if test "$expat" = "yes" -a "$expat_includes" = "yes" -a "$expat_lib" = "yes"
+then
+  PKG_CHECK_MODULES(expat, expat, [
+      expat=`${PKG_CONFIG} --variable=prefix expat`
+      expat_includes="pkg-config"
+      expat_lib="pkg-config"
+      AC_MSG_WARN([expat in ${expat} will be used])
+    ],[
+      AC_MSG_WARN([pkg-config cannot find expat])
+    ]
+  )
+fi
+
 if test "$enable_libxml2" != "yes"; then
 	case "$expat" in
 	no)
 	;;
 	*)
 		case "$expat_includes" in
+		pkg-config)
+			EXPAT_CFLAGS=`${PKG_CONFIG} --cflags expat`
+			;;
 		yes)
 			case "$expat" in
 			yes)
@@ -269,6 +288,9 @@ if test "$enable_libxml2" != "yes"; then
 			;;
 		esac
 		case "$expat_lib" in
+		pkg-config)
+			EXPAT_LIBS=`${PKG_CONFIG} --libs expat`
+			;;
 		yes)
 			case "$expat" in
 			yes)
@@ -317,8 +339,8 @@ if test "$enable_libxml2" != "yes"; then
 			expat=no
 			;;
 		yes)
-			AC_CHECK_FUNCS(XML_SetDoctypeDeclHandler)
-			case "$ac_cv_func_XML_SetDoctypeDeclHandler" in
+			AC_CHECK_LIB(expat, XML_SetDoctypeDeclHandler)
+			case "$ac_cv_lib_expat_XML_SetDoctypeDeclHandler" in
 			yes)
 				HAVE_EXPAT=1
 				AC_SUBST(HAVE_EXPAT)
@@ -355,8 +377,6 @@ fi
 
 AC_ARG_ENABLE(libxml2,         [  --enable-libxml2              Use libxml2 instead of Expat])
 
-PKG_PROG_PKG_CONFIG
-
 if test "$enable_libxml2" = "yes" -o "$expat" = "no"; then
     PKG_CHECK_MODULES([LIBXML2], [libxml-2.0 >= 2.6])
     AC_DEFINE_UNQUOTED(ENABLE_LIBXML2,1,[Use libxml2 instead of Expat])