diff --git a/pngconf.h b/pngconf.h
index a566d3952..db99dba96 100644
--- a/pngconf.h
+++ b/pngconf.h
@@ -8,6 +8,7 @@
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  *
  * This code is released under the zlib-libpng license.
+ * For conditions of distribution and use, see copyright notice in png.h
  *
  */
 
diff --git a/pngpriv.h b/pngpriv.h
index 7c034378a..33d1e97cb 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -8,6 +8,7 @@
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  *
  * This code is released under the zlib-libpng license.
+ * For conditions of distribution and use, see copyright notice in png.h
  *
  */