diff --git a/scheme/lib/uri.scm b/scheme/lib/uri.scm
index bc796d1..643573d 100644
--- a/scheme/lib/uri.scm
+++ b/scheme/lib/uri.scm
@@ -116,8 +116,10 @@
 ;;; slashes and colons would be escaped.
 
 (define uri-escaped-chars
-  (char-set-complement (char-set-union char-set:letter+digit
-				       (string->char-set "$-_@.&!*\"'(),+"))))
+  (char-set-complement 
+   ;; RFC 2396 (URI Generic Syntax) specifies unreserved = alphanum | mark
+   (char-set-union char-set:letter+digit
+                   (string->char-set "-_.!~*'()"))))
 
 ;;; Takes a set of chars to escape. This is because we sometimes need to
 ;;; escape larger sets of chars for different parts of a URI.