diff --git a/NEWS b/NEWS
index dca8db6eba1..9ef2f169182 100644
--- a/NEWS
+++ b/NEWS
@@ -73,6 +73,10 @@ PHP                                                                        NEWS
     encoded words as required by RFC 2047; they are converted to spaces.
     Underscores must be encoded as "=5F" in such MIME encoded words.
     (Alex Dowad)
+  . mb_encode_mimeheader no longer drops NUL (zero) bytes when
+    QPrint-encoding the input string. This previously caused strings in
+    certain text encodings, especially UTF-16 and UTF-32, to be
+    corrupted by mb_encode_mimeheader. (Alex Dowad)
 
 - mysqli:
   . mysqli_fetch_object raises a ValueError instead of an Exception.
diff --git a/UPGRADING b/UPGRADING
index 210215c3fab..db2fdaaa50e 100644
--- a/UPGRADING
+++ b/UPGRADING
@@ -91,6 +91,9 @@ PHP 8.3 UPGRADE NOTES
     encoded words as required by RFC 2047; they are converted to spaces.
     Underscores must be encoded as "=5F" in such MIME encoded words.
     (Alex Dowad)
+  . In rare cases, mb_encode_mimeheader will transfer-encode its input
+    string where it would pass it through as raw ASCII in PHP 8.2.
+    (Alex Dowad)
 
 - mysqli:
   . mysqli_fetch_object now raises a ValueError instead of an Exception when the constructor_args