Index: src/wp-admin/link-parse-opml.php
===================================================================
--- src/wp-admin/link-parse-opml.php	(revision 38368)
+++ src/wp-admin/link-parse-opml.php	(working copy)
@@ -72,6 +72,9 @@
 }
 
 // Create an XML parser
+if ( ! function_exists( 'xml_parser_create' ) ) {
+	trigger_error( __( "PHP's XML extension is not available. Please contact your hosting provider to enable PHP's XML extension." ) );
+}
 $xml_parser = xml_parser_create();
 
 // Set the functions to handle opening and closing tags
Index: src/wp-includes/atomlib.php
===================================================================
--- src/wp-includes/atomlib.php	(revision 38368)
+++ src/wp-includes/atomlib.php	(working copy)
@@ -121,6 +121,10 @@
 
         array_unshift($this->ns_contexts, array());
 
+        if ( ! function_exists( 'xml_parser_create' ) ) {
+        	trigger_error( __( "PHP's XML extension is not available. Please contact your hosting provider to enable PHP's XML extension." ) );
+        }
+
         $parser = xml_parser_create_ns();
         xml_set_object($parser, $this);
         xml_set_element_handler($parser, "start_element", "end_element");
Index: src/wp-includes/class-IXR.php
===================================================================
--- src/wp-includes/class-IXR.php	(revision 38368)
+++ src/wp-includes/class-IXR.php	(working copy)
@@ -219,8 +219,11 @@
 		self::__construct( $message );
 	}
 
-    function parse()
-    {
+    function parse() {
+        if ( ! function_exists( 'xml_parser_create' ) ) {
+            trigger_error( __( "PHP's XML extension is not available. Please contact your hosting provider to enable PHP's XML" ) );
+        }
+
         // first remove the XML declaration
         // merged from WP #10698 - this method avoids the RAM usage of preg_replace on very large messages
         $header = preg_replace( '/<\?xml.*?\?'.'>/s', '', substr( $this->message, 0, 100 ), 1 );
@@ -1220,3 +1223,4 @@
         return parent::query('system.multicall', $this->calls);
     }
 }
+
Index: src/wp-includes/feed.php
===================================================================
--- src/wp-includes/feed.php	(revision 38368)
+++ src/wp-includes/feed.php	(working copy)
@@ -538,6 +538,10 @@
 		return array('text', $data);
 	}
 
+	if ( ! function_exists( 'xml_parser_create' ) ) {
+		trigger_error( __( "PHP's XML extension is not available. Please contact your hosting provider to enable PHP's XML extension." ) );
+	}
+
 	$parser = xml_parser_create();
 	xml_parse($parser, '<div>' . $data . '</div>', true);
 	$code = xml_get_error_code($parser);