diff --git a/XMLCONF b/XMLCONF
index 84212c9..3b4976d 100644
--- a/XMLCONF
+++ b/XMLCONF
@@ -167,13 +167,7 @@ xmltest/not-wf/sa/166.xml [not validating:] not-wf [validating:] invalid
 xmltest/not-wf/sa/167.xml [not validating:] not-wf [validating:] invalid
 xmltest/not-wf/sa/168.xml [not validating:] not-wf [validating:] invalid
 xmltest/not-wf/sa/169.xml [not validating:] not-wf [validating:] invalid
-xmltest/not-wf/sa/170.xml [not validating:] FAILED:
-  well-formedness violation not detected
-[
-    Four byte UTF-8 encodings can encode UCS-4 characters
-    which are beyond the range of legal XML characters
-    (and can't be expressed in Unicode surrogate pairs).
-    This document holds such a character.  ]
+xmltest/not-wf/sa/170.xml [not validating:] not-wf [validating:] invalid
 xmltest/not-wf/sa/171.xml [not validating:] FAILED:
   well-formedness violation not detected
 [
@@ -1862,4 +1856,4 @@ ibm/valid/P86/ibm86v01.xml [not validating:] input [validating:] input
 ibm/valid/P87/ibm87v01.xml [not validating:] input [validating:] input
 ibm/valid/P88/ibm88v01.xml [not validating:] input [validating:] input
 ibm/valid/P89/ibm89v01.xml [not validating:] input [validating:] input
-15/1786 tests failed; 376 tests were skipped
\ No newline at end of file
+14/1786 tests failed; 376 tests were skipped
\ No newline at end of file
diff --git a/runes/encodings.lisp b/runes/encodings.lisp
index 04ddd93..bdd8e99 100644
--- a/runes/encodings.lisp
+++ b/runes/encodings.lisp
@@ -160,8 +160,10 @@
                  `((lambda (x)
                      (when (or (<= #xD800 x #xDBFF)
 			       (<= #xDC00 x #xDFFF))
-		       (xerror "surrogate encoded in UTF-8: #x~x." x))
-                     (cond ((%> x #xFFFF)
+		       (xerror "surrogate encoded in UTF-8: #x~X." x))
+                     (cond ((%> x #x10FFFF)
+                            (xerror "not a valid code point: #x~X" x))
+		           ((%> x #xFFFF)
                             (setf (aref out (%+ 0 wptr)) (%+ #xD7C0 (ash x -10))
                                   (aref out (%+ 1 wptr)) (%ior #xDC00 (%and x #x3FF)))
                             (setf wptr (%+ wptr 2)))