diff --git a/UPGRADING b/UPGRADING
index e2e17e62390ef..4bd56032f321d 100644
--- a/UPGRADING
+++ b/UPGRADING
@@ -311,9 +311,10 @@ PHP 8.0 UPGRADE NOTES
     warning.
 
 - GD:
-  . The GD extension now uses objects as the underlying data structure for
+  . The GD extension now uses a GdImage object as the underlying data structure for
     images, rather than resources. These objects are completely opaque, i.e.
-    they don't have any methods.
+    they don't have any methods. Return value checks using is_resource() should be
+    replaced with checks for `false`.
   . The deprecated function image2wbmp() has been removed.
     RFC: https://wiki.php.net/rfc/image2wbmp
   . The deprecated functions png2wbmp() and jpeg2wbmp() have been removed.