*** a/src/backend/utils/adt/xml.c
--- b/src/backend/utils/adt/xml.c
***************
*** 141,149 **** static bool print_xml_decl(StringInfo buf, const xmlChar *version,
  			   pg_enc encoding, int standalone);
  static xmlDocPtr xml_parse(text *data, XmlOptionType xmloption_arg,
  		  bool preserve_whitespace, int encoding);
! static text *xml_xmlnodetoxmltype(xmlNodePtr cur);
  static int xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
! 					   ArrayBuildState **astate);
  #endif   /* USE_LIBXML */
  
  static StringInfo query_to_xml_internal(const char *query, char *tablename,
--- 141,151 ----
  			   pg_enc encoding, int standalone);
  static xmlDocPtr xml_parse(text *data, XmlOptionType xmloption_arg,
  		  bool preserve_whitespace, int encoding);
! static text *xml_xmlnodetoxmltype(xmlNodePtr cur,
! 					   PgXmlErrorContext *xmlerrcxt);
  static int xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
! 					   ArrayBuildState **astate,
! 					   PgXmlErrorContext *xmlerrcxt);
  #endif   /* USE_LIBXML */
  
  static StringInfo query_to_xml_internal(const char *query, char *tablename,
***************
*** 3595,3620 **** SPI_sql_row_to_xmlelement(int rownum, StringInfo result, char *tablename,
   * return value otherwise)
   */
  static text *
! xml_xmlnodetoxmltype(xmlNodePtr cur)
  {
  	xmltype    *result;
  
  	if (cur->type == XML_ELEMENT_NODE)
  	{
  		xmlBufferPtr buf;
  
  		buf = xmlBufferCreate();
  		PG_TRY();
  		{
! 			xmlNodeDump(buf, NULL, cur, 0, 1);
  			result = xmlBuffer_to_xmltype(buf);
  		}
  		PG_CATCH();
  		{
  			xmlBufferFree(buf);
  			PG_RE_THROW();
  		}
  		PG_END_TRY();
  		xmlBufferFree(buf);
  	}
  	else
--- 3597,3636 ----
   * return value otherwise)
   */
  static text *
! xml_xmlnodetoxmltype(xmlNodePtr cur, PgXmlErrorContext *xmlerrcxt)
  {
  	xmltype    *result;
  
  	if (cur->type == XML_ELEMENT_NODE)
  	{
  		xmlBufferPtr buf;
+ 		xmlNodePtr cur_copy;
  
  		buf = xmlBufferCreate();
+ 
+ 		/* the result of xmlNodeDump won't contain namespace definitions
+ 		 * from parent nodes, but xmlCopyNode duplicates a node along
+ 		 * with its required namespace definitions.
+ 		 */
+ 		cur_copy = xmlCopyNode(cur, 1);
+ 
+ 		if (cur_copy == NULL)
+ 			xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
+ 						"could not serialize xml");
+ 
  		PG_TRY();
  		{
! 			xmlNodeDump(buf, NULL, cur_copy, 0, 1);
  			result = xmlBuffer_to_xmltype(buf);
  		}
  		PG_CATCH();
  		{
+ 			xmlFreeNode(cur_copy);
  			xmlBufferFree(buf);
  			PG_RE_THROW();
  		}
  		PG_END_TRY();
+ 		xmlFreeNode(cur_copy);
  		xmlBufferFree(buf);
  	}
  	else
***************
*** 3656,3662 **** xml_xmlnodetoxmltype(xmlNodePtr cur)
   */
  static int
  xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
! 					   ArrayBuildState **astate)
  {
  	int			result = 0;
  	Datum		datum;
--- 3672,3679 ----
   */
  static int
  xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
! 					   ArrayBuildState **astate,
! 					   PgXmlErrorContext *xmlerrcxt)
  {
  	int			result = 0;
  	Datum		datum;
***************
*** 3678,3684 **** xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
  
  					for (i = 0; i < result; i++)
  					{
! 						datum = PointerGetDatum(xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i]));
  						*astate = accumArrayResult(*astate, datum,
  												   false, XMLOID,
  												   CurrentMemoryContext);
--- 3695,3702 ----
  
  					for (i = 0; i < result; i++)
  					{
! 						datum = PointerGetDatum(xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i],
! 																	 xmlerrcxt));
  						*astate = accumArrayResult(*astate, datum,
  												   false, XMLOID,
  												   CurrentMemoryContext);
***************
*** 3882,3890 **** xpath_internal(text *xpath_expr_text, xmltype *data, ArrayType *namespaces,
  		 * Extract the results as requested.
  		 */
  		if (res_nitems != NULL)
! 			*res_nitems = xml_xpathobjtoxmlarray(xpathobj, astate);
  		else
! 			(void) xml_xpathobjtoxmlarray(xpathobj, astate);
  	}
  	PG_CATCH();
  	{
--- 3900,3908 ----
  		 * Extract the results as requested.
  		 */
  		if (res_nitems != NULL)
! 			*res_nitems = xml_xpathobjtoxmlarray(xpathobj, astate, xmlerrcxt);
  		else
! 			(void) xml_xpathobjtoxmlarray(xpathobj, astate, xmlerrcxt);
  	}
  	PG_CATCH();
  	{
*** a/src/test/regress/expected/xml.out
--- b/src/test/regress/expected/xml.out
***************
*** 584,589 **** SELECT xpath('//loc:piece/@id', '<local:data xmlns:local="http://127.0.0.1"><loc
--- 584,595 ----
   {1,2}
  (1 row)
  
+ SELECT xpath('//loc:piece', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number one</local:piece><local:piece id="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]);
+                                                                      xpath                                                                      
+ ------------------------------------------------------------------------------------------------------------------------------------------------
+  {"<local:piece xmlns:local=\"http://127.0.0.1\" id=\"1\">number one</local:piece>","<local:piece xmlns:local=\"http://127.0.0.1\" id=\"2\"/>"}
+ (1 row)
+ 
  SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
            xpath          
  -------------------------
*** a/src/test/regress/expected/xml_1.out
--- b/src/test/regress/expected/xml_1.out
***************
*** 498,503 **** LINE 1: SELECT xpath('//loc:piece/@id', '<local:data xmlns:local="ht...
--- 498,509 ----
                                          ^
  DETAIL:  This functionality requires the server to be built with libxml support.
  HINT:  You need to rebuild PostgreSQL using --with-libxml.
+ SELECT xpath('//loc:piece', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number one</local:piece><local:piece id="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]);
+ ERROR:  unsupported XML feature
+ LINE 1: SELECT xpath('//loc:piece', '<local:data xmlns:local="http:/...
+                                     ^
+ DETAIL:  This functionality requires the server to be built with libxml support.
+ HINT:  You need to rebuild PostgreSQL using --with-libxml.
  SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
  ERROR:  unsupported XML feature
  LINE 1: SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>'...
*** a/src/test/regress/sql/xml.sql
--- b/src/test/regress/sql/xml.sql
***************
*** 174,179 **** SELECT xpath(NULL, NULL) IS NULL FROM xmltest;
--- 174,180 ----
  SELECT xpath('', '<!-- error -->');
  SELECT xpath('//text()', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number one</local:piece><local:piece id="2" /></local:data>');
  SELECT xpath('//loc:piece/@id', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number one</local:piece><local:piece id="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]);
+ SELECT xpath('//loc:piece', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number one</local:piece><local:piece id="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]);
  SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
  SELECT xpath('//text()', '<root>&lt;</root>');
  SELECT xpath('//@value', '<root value="&lt;"/>');