diff --git a/pngpriv.h b/pngpriv.h
index 150a4fa4b..a2423a32d 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -1,9 +1,9 @@
 
 /* pngpriv.h - private declarations for use inside libpng
  *
- * libpng version 1.4.20 - December 29, 2016
+ * libpng version 1.4.21beta01 - August 7, 2017
  * For conditions of distribution and use, see copyright notice in png.h
- * Copyright (c) 1998-2002,2004,2006-2014 Glenn Randers-Pehrson
+ * Copyright (c) 1998-2002,2004,2006-2014,2017 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  *
@@ -752,6 +752,9 @@ PNG_EXTERN void png_handle_unknown PNGARG((png_structp png_ptr,
 PNG_EXTERN void png_check_chunk_name PNGARG((png_structp png_ptr,
    png_bytep chunk_name));
 
+PNG_EXTERN void png_check_chunk_length PNGARG((png_structp png_ptr,
+   png_uint_32 chunk_length));
+
 /* Handle the transformations for reading and writing */
 PNG_EXTERN void png_do_read_transformations PNGARG((png_structp png_ptr));
 PNG_EXTERN void png_do_write_transformations PNGARG((png_structp png_ptr));
diff --git a/pngread.c b/pngread.c
index 1e0ac4300..a2ef93537 100644
--- a/pngread.c
+++ b/pngread.c
@@ -1,8 +1,8 @@
 
 /* pngread.c - read a PNG file
  *
- * Last changed in libpng 1.4.14 [November 20, 2014]
- * Copyright (c) 1998-2002,2004,2006-2014 Glenn Randers-Pehrson
+ * Last changed in libpng 1.4.21 [August 7, 2017]
+ * Copyright (c) 1998-2002,2004,2006-2014,2017 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  *
diff --git a/pngrutil.c b/pngrutil.c
index 98ad5115e..aa64ae0c4 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -1,8 +1,8 @@
 
 /* pngrutil.c - utilities to read a PNG file
  *
- * Last changed in libpng 1.4.18 [December 11, 2015]
- * Copyright (c) 1998-2002,2004,2006-2015 Glenn Randers-Pehrson
+ * Last changed in libpng 1.4.21 [August 7, 2017]
+ * Copyright (c) 1998-2002,2004,2006-2015,2017 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  *