diff --git a/NEWS b/NEWS
index c10ef7b24c4..aa539b4f407 100644
--- a/NEWS
+++ b/NEWS
@@ -165,6 +165,7 @@ PHP                                                                        NEWS
     is now a boolean. (David Carlier)
   . Fixed bug GH-16883 (gzopen() does not use the default stream context when
     opening HTTP URLs). (nielsdos)
+  . Implemented GH-17668 (zlib streams should support locking). (nielsdos)
 
 
 <<< NOTE: Insert NEWS from last stable release here prior to actual release! >>>
diff --git a/UPGRADING b/UPGRADING
index eca064f3e48..86b3dfe66ad 100644
--- a/UPGRADING
+++ b/UPGRADING
@@ -107,6 +107,10 @@ PHP 8.5 UPGRADE NOTES
     and is not a QName because in those cases the namespace is taken
     from the namespace href or prefix respectively.
 
+- Zlib:
+  . flock() is now supported on zlib streams. Previously, this always
+    failed to perform any locking action.
+
 ========================================
 3. Changes in SAPI modules
 ========================================