diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index e770c1cf11..7f1cb36724 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -10,6 +10,8 @@
   for Gray streams.
 * Generic versions of `cl:pathname` and `cl:truename`, both of which
   are available after the Gray stream modules is required.
+* Generic `(setf gray:stream-element-type)` for basic support of
+  bivalent streams.
 
 ## Changed
 * `cl:format` and `pprint` now respect the value returned bye
diff --git a/src/lisp/kernel/clos/streams.lisp b/src/lisp/kernel/clos/streams.lisp
index 87ca98d77a..1cf2c5f98e 100644
--- a/src/lisp/kernel/clos/streams.lisp
+++ b/src/lisp/kernel/clos/streams.lisp
@@ -55,6 +55,12 @@
   STREAM. The class FUNDAMENTAL-CHARACTER-STREAM provides a default method
   which returns CHARACTER."))
 
+(defgeneric (setf stream-element-type) (new-value stream)
+  (:documentation
+   "Set the type specifier of the kind of object returned by the
+  STREAM. There is no default method as this is optional and only
+  needed for bivalent streams."))
+
 (defgeneric stream-finish-output (stream)
   (:documentation
    "Attempts to ensure that all output sent to the Stream has reached