Index: wp-includes/class-simplepie.php
===================================================================
--- wp-includes/class-simplepie.php	(revision 12371)
+++ wp-includes/class-simplepie.php	(working copy)
@@ -9440,6 +9440,10 @@
 		{
 			return $return;
 		}
+		// Server has neither of mb_convert_encoding() or iconv(). Maybe there's nothing to convert?
+		elseif ( $input == $output ) {
+			return $data;
+		}
 		// If we can't do anything, just fail
 		else
 		{