diff --git a/glib/gunicollate.c b/glib/gunicollate.c
index af4179571..3ec254d65 100644
--- a/glib/gunicollate.c
+++ b/glib/gunicollate.c
@@ -372,11 +372,16 @@ carbon_collate_key_for_filename (const gchar *str,
  * The results of comparing the collation keys of two strings 
  * with strcmp() will always be the same as comparing the two 
  * original keys with g_utf8_collate().
- * 
+ *
  * Note that this function depends on the [current locale][setlocale].
+ *
+ * Note that the returned string is not guaranteed to be in any
+ * encoding, especially UTF-8. The returned value is meant to be
+ * used only for comparisons.
  * 
- * Returns: a newly allocated string. This string should
- *   be freed with g_free() when you are done with it.
+ * Returns: (transfer full) (type filename): a newly allocated string.
+ *   The contents of the string are only meant to be used when sorting.
+ *   This string should be freed with g_free() when you are done with it.
  **/
 gchar *
 g_utf8_collate_key (const gchar *str,
@@ -504,8 +509,13 @@ g_utf8_collate_key (const gchar *str,
  * 
  * Note that this function depends on the [current locale][setlocale].
  *
- * Returns: a newly allocated string. This string should
- *   be freed with g_free() when you are done with it.
+ * Note that the returned string is not guaranteed to be in any
+ * encoding, especially UTF-8. The returned value is meant to be
+ * used only for comparisons.
+ *
+ * Returns: (transfer full) (type filename): a newly allocated string.
+ *   The contents of the string are only meant to be used when sorting.
+ *   This string should be freed with g_free() when you are done with it.
  *
  * Since: 2.8
  */