diff --git a/ANNOUNCE b/ANNOUNCE
index 293f396cb..bf6522f60 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -212,6 +212,10 @@ version 1.5.0beta23 [April 29, 2010]
   Corrected protection of png_get_user_transform_ptr. The API declaration in
     png.h is removed if both READ and WRITE USER_TRANSFORM are turned off
     but was left defined in pngtrans.c
+  Added logunsupported=1 to cause pnglibconf.h to document disabled options.
+    This makes the installed pnglibconf.h more readable but causes no
+    other change.  The intention is that users of libpng will find it
+    easier to understand if an API they need is missing.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net:
 (subscription required; visit
diff --git a/CHANGES b/CHANGES
index 090e4fbd8..740e19b67 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2694,6 +2694,10 @@ version 1.5.0beta23 [April 29, 2010]
   Corrected protection of png_get_user_transform_ptr. The API declaration in
     png.h is removed if both READ and WRITE USER_TRANSFORM are turned off
     but was left defined in pngtrans.c
+  Added logunsupported=1 to cause pnglibconf.h to document disabled options.
+    This makes the installed pnglibconf.h more readable but causes no
+    other change.  The intention is that users of libpng will find it
+    easier to understand if an API they need is missing.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/scripts/pnglibconf.dfa b/scripts/pnglibconf.dfa
index 708f55337..ea052293d 100644
--- a/scripts/pnglibconf.dfa
+++ b/scripts/pnglibconf.dfa
@@ -6,7 +6,7 @@
 #
 com pnglibconf.h - library build configuration
 com
-com libpng version PNGLIB_VERSION - last changed on April 28, 2010
+com libpng version PNGLIB_VERSION - last changed on April 29, 2010
 com
 com Copyright (c) 1998-2010 Glenn Randers-Pehrson
 com
@@ -99,6 +99,11 @@ file pnglibconf.h scripts/pnglibconf.dfa PNGLCONF_H
 # libpng and need new or modified options/settings.
 #----------------------------------------------------------------------
 
+# The following causes commented out #undef lines to be written to
+# pnglibconf.h, this can be stopped by logunsupported=0 in a later
+# file or on the command line (after pnglibconf.dfa)
+logunsupported = 1
+
 # PNG_USER_CONFIG has to be defined on the compiler command line
 # to cause pngusr.h to be read while constructing pnglibconf.h
 #