diff --git a/LICENSE b/LICENSE
index 2151113..7735d65 100644
--- a/LICENSE
+++ b/LICENSE
@@ -10,7 +10,7 @@
 
 This code is released under the libpng license.
 
-libpng versions 1.0.7, July 1, 2000 through 1.7.0beta88, April 1, 2017 are
+libpng versions 1.0.7, July 1, 2000 through 1.7.0beta88, August 6, 2017 are
 Copyright (c) 2000-2002, 2004, 2006-2017 Glenn Randers-Pehrson, are
 derived from libpng-1.0.6, and are distributed according to the same
 disclaimer and license as libpng-1.0.6 with the following individuals
@@ -127,4 +127,4 @@
 
 Glenn Randers-Pehrson
 glennrp at users.sourceforge.net
-April 1, 2017
+August 6, 2017
diff --git a/README b/README
index 174d5ad..c33f5f6 100644
--- a/README
+++ b/README
@@ -1,4 +1,4 @@
-README for libpng version 1.7.0beta88 - May 22, 2017 (shared library 17.0)
+README for libpng version 1.7.0beta88 - August 6, 2017 (shared library 17.0)
 See the note about version numbers near the top of png.h
 
 See INSTALL for instructions on how to install libpng.
diff --git a/contrib/gregbook/README b/contrib/gregbook/README
index edaf2b7..171c5fd 100644
--- a/contrib/gregbook/README
+++ b/contrib/gregbook/README
@@ -63,7 +63,7 @@
 
  - Prerequisites (in order of compilation):
 
-      - zlib            http://zlib.net/
+      - zlib            https://zlib.net/
       - libpng          http://www.libpng.org/pub/png/libpng.html
       - pngbook         http://www.libpng.org/pub/png/book/sources.html
 
diff --git a/contrib/libtests/pngstest.c b/contrib/libtests/pngstest.c
index 30f57a9..ab45089 100644
--- a/contrib/libtests/pngstest.c
+++ b/contrib/libtests/pngstest.c
@@ -1,9 +1,8 @@
 /*-
  * pngstest.c
  *
- * Copyright (c) 2013-2016 John Cunningham Bowler
- *
- * Last changed in libpng 1.6.24 [August 4, 2016]
+ * Last changed in libpng 1.6.31 [July 27, 2017]
+ * Copyright (c) 2013-2017 John Cunningham Bowler
  *
  * This code is released under the libpng license.
  * For conditions of distribution and use, see the disclaimer
@@ -2611,9 +2610,9 @@
    const unsigned int b_sample = PNG_IMAGE_SAMPLE_SIZE(formatb);
    int alpha_added, alpha_removed;
    int bchannels;
-   int btoa[4];
    png_uint_32 y;
    Transform tr;
+   int btoa[4]={0,0,0,0};
 
    /* This should never happen: */
    if (width != b->image.width || height != b->image.height)
@@ -2746,22 +2745,27 @@
        */
       else if ((a->opts & ACCUMULATE) == 0)
       {
+#        ifdef __GNUC__
+#           define BYTE_CHARS 20 /* 2^32: GCC sprintf warning */
+#        else
+#           define BYTE_CHARS 3 /* 2^8: real maximum value */
+#        endif
          /* Check the original image first,
           * TODO: deal with input images with bad pixel values?
           */
          if (amax >= a->image.colormap_entries)
          {
-            char pindex[9];
-            sprintf(pindex, "%d[%lu]", amax,
-               (unsigned long)a->image.colormap_entries);
+            char pindex[3+2*BYTE_CHARS];
+            sprintf(pindex, "%d[%u]", amax,
+               (png_byte)/*SAFE*/a->image.colormap_entries);
             return logerror(a, a->file_name, ": bad pixel index: ", pindex);
          }
 
          else if (bmax >= b->image.colormap_entries)
          {
-            char pindex[9];
-            sprintf(pindex, "%d[%lu]", bmax,
-               (unsigned long)b->image.colormap_entries);
+            char pindex[3+2*BYTE_CHARS];
+            sprintf(pindex, "%d[%u]", bmax,
+               (png_byte)/*SAFE*/b->image.colormap_entries);
             return logerror(b, b->file_name, ": bad pixel index: ", pindex);
          }
       }
@@ -2881,10 +2885,13 @@
                {
                   case 4:
                      if (pua[btoa[3]] != pub[3]) break;
+                     /* FALLTHROUGH */
                   case 3:
                      if (pua[btoa[2]] != pub[2]) break;
+                     /* FALLTHROUGH */
                   case 2:
                      if (pua[btoa[1]] != pub[1]) break;
+                     /* FALLTHROUGH */
                   case 1:
                      if (pua[btoa[0]] != pub[0]) break;
                      if (alpha_added != 4 && pub[alpha_added] != 65535) break;
@@ -2900,10 +2907,13 @@
                {
                   case 4:
                      if (psa[btoa[3]] != psb[3]) break;
+                     /* FALLTHROUGH */
                   case 3:
                      if (psa[btoa[2]] != psb[2]) break;
+                     /* FALLTHROUGH */
                   case 2:
                      if (psa[btoa[1]] != psb[1]) break;
+                     /* FALLTHROUGH */
                   case 1:
                      if (psa[btoa[0]] != psb[0]) break;
                      if (alpha_added != 4 && psb[alpha_added] != 255) break;
diff --git a/libpng-manual.txt b/libpng-manual.txt
index 172aa71..5794f65 100644
--- a/libpng-manual.txt
+++ b/libpng-manual.txt
@@ -1,6 +1,6 @@
 libpng-manual.txt - A description on how to use and modify libpng
 
- libpng version 1.7.0beta88 - May 22, 2017
+ libpng version 1.7.0beta88 - August 6, 2017
  Updated and distributed by Glenn Randers-Pehrson
  <glennrp at users.sourceforge.net>
  Copyright (c) 1998-2017 Glenn Randers-Pehrson
@@ -11,7 +11,7 @@
 
  Based on:
 
- libpng versions 0.97, January 1998, through 1.7.0beta88 - May 22, 2017
+ libpng versions 0.97, January 1998, through 1.7.0beta88 - August 6, 2017
  Updated and distributed by Glenn Randers-Pehrson
  Copyright (c) 1998-2015 Glenn Randers-Pehrson
 
@@ -102,7 +102,7 @@
 
 Libpng uses zlib for its compression and decompression of PNG files.
 Further information about zlib, and the latest version of zlib, can
-be found at the zlib home page, <http://zlib.net/>.
+be found at the zlib home page, <https://zlib.net/>.
 The zlib compression utility is a general purpose utility that is
 useful for more than PNG files, and can be used without libpng.
 See the documentation delivered with zlib for more details.
@@ -5189,11 +5189,13 @@
 going back to version 0.70.  You can access the git repository (read only)
 at
 
-    git://git.code.sf.net/p/libpng/code.git
+    https://github.com/glennrp/libpng or
+    https://git.code.sf.net/p/libpng/code.git
 
-or you can browse it with a web browser by selecting the "code" button at
+or you can browse it with a web browser at
 
-    https://sourceforge.net/projects/libpng
+    https://github.com/glennrp/libpng or
+    https://sourceforge.net/p/libpng/code/ci/libpng16/tree/
 
 Patches can be sent to glennrp at users.sourceforge.net or to
 png-mng-implement at lists.sourceforge.net or you can upload them to
@@ -5201,10 +5203,14 @@
 
     https://libpng.sourceforge.io/
 
+or as a "pull request" to
+
+    https://github.com/glennrp/libpng/pulls
+
 We also accept patches built from the tar or zip distributions, and
 simple verbal discriptions of bug fixes, reported either to the
 SourceForge bug tracker, to the png-mng-implement at lists.sf.net
-mailing list, or directly to glennrp.
+mailing list, as github issues, or directly to glennrp.
 
 XVI. Coding style
 
diff --git a/libpng.3 b/libpng.3
index a1b3fc0..f33e5d2 100644
--- a/libpng.3
+++ b/libpng.3
@@ -1,4 +1,4 @@
-.TH LIBPNG 3 "May 22, 2017"
+.TH LIBPNG 3 "August 6, 2017"
 .SH NAME
 libpng \- Portable Network Graphics (PNG) Reference Library 1.7.0beta88
 .SH SYNOPSIS
@@ -500,7 +500,7 @@
 .SH LIBPNG.TXT
 libpng-manual.txt - A description on how to use and modify libpng
 
- libpng version 1.7.0beta88 - May 22, 2017
+ libpng version 1.7.0beta88 - August 6, 2017
  Updated and distributed by Glenn Randers-Pehrson
  <glennrp at users.sourceforge.net>
  Copyright (c) 1998-2017 Glenn Randers-Pehrson
@@ -511,7 +511,7 @@
 
  Based on:
 
- libpng versions 0.97, January 1998, through 1.7.0beta88 - May 22, 2017
+ libpng versions 0.97, January 1998, through 1.7.0beta88 - August 6, 2017
  Updated and distributed by Glenn Randers-Pehrson
  Copyright (c) 1998-2015 Glenn Randers-Pehrson
 
@@ -602,7 +602,7 @@
 
 Libpng uses zlib for its compression and decompression of PNG files.
 Further information about zlib, and the latest version of zlib, can
-be found at the zlib home page, <http://zlib.net/>.
+be found at the zlib home page, <https://zlib.net/>.
 The zlib compression utility is a general purpose utility that is
 useful for more than PNG files, and can be used without libpng.
 See the documentation delivered with zlib for more details.
@@ -5689,11 +5689,13 @@
 going back to version 0.70.  You can access the git repository (read only)
 at
 
-    git://git.code.sf.net/p/libpng/code.git
+    https://github.com/glennrp/libpng or
+    https://git.code.sf.net/p/libpng/code.git
 
-or you can browse it with a web browser by selecting the "code" button at
+or you can browse it with a web browser at
 
-    https://sourceforge.net/projects/libpng
+    https://github.com/glennrp/libpng or
+    https://sourceforge.net/p/libpng/code/ci/libpng16/tree/
 
 Patches can be sent to glennrp at users.sourceforge.net or to
 png-mng-implement at lists.sourceforge.net or you can upload them to
@@ -5701,10 +5703,14 @@
 
     https://libpng.sourceforge.io/
 
+or as a "pull request" to
+
+    https://github.com/glennrp/libpng/pulls
+
 We also accept patches built from the tar or zip distributions, and
 simple verbal discriptions of bug fixes, reported either to the
 SourceForge bug tracker, to the png-mng-implement at lists.sf.net
-mailing list, or directly to glennrp.
+mailing list, as github issues, or directly to glennrp.
 
 .SH XVI. Coding style
 
@@ -5991,7 +5997,7 @@
 .I libpng
 or at
 .br
-http://zlib.net/
+https://zlib.net/
 
 .LP
 .IR PNG specification: RFC 2083
@@ -6020,7 +6026,7 @@
 
 Thanks to Frank J. T. Wojcik for helping with the documentation.
 
-Libpng version 1.7.0beta88 - May 22, 2017:
+Libpng version 1.7.0beta88 - August 6, 2017:
 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
 
@@ -6045,7 +6051,7 @@
 
 This code is released under the libpng license.
 
-libpng versions 1.0.7, July 1, 2000 through 1.7.0beta88, May 22, 2017 are
+libpng versions 1.0.7, July 1, 2000 through 1.7.0beta88, August 6, 2017 are
 Copyright (c) 2000-2002, 2004, 2006-2017 Glenn Randers-Pehrson, are
 derived from libpng-1.0.6, and are distributed according to the same
 disclaimer and license as libpng-1.0.6 with the following individuals
@@ -6170,7 +6176,7 @@
 
 Glenn Randers-Pehrson
 glennrp at users.sourceforge.net
-May 22, 2017
+August 6, 2017
 
 .\" end of man page
 
diff --git a/libpngpf.3 b/libpngpf.3
index 3c7db65..4053c65 100644
--- a/libpngpf.3
+++ b/libpngpf.3
@@ -1,4 +1,4 @@
-.TH LIBPNGPF 3 "April 1, 2017"
+.TH LIBPNGPF 3 "August 6, 2017"
 .SH NAME
 libpng \- Portable Network Graphics (PNG) Reference Library 1.7.0beta88
 (private functions)
diff --git a/png.5 b/png.5
index 4fdc9f0..40a450f 100644
--- a/png.5
+++ b/png.5
@@ -1,4 +1,4 @@
-.TH PNG 5 "April 1, 2017"
+.TH PNG 5 "August 6, 2017"
 .SH NAME
 png \- Portable Network Graphics (PNG) format
 .SH DESCRIPTION
diff --git a/png.c b/png.c
index af0bdc8..68f5bbd 100644
--- a/png.c
+++ b/png.c
@@ -705,14 +705,14 @@
 #else
 #  ifdef __STDC__
    return PNG_STRING_NEWLINE \
-     "libpng version 1.7.0beta88 - April 1, 2017" PNG_STRING_NEWLINE \
+     "libpng version 1.7.0beta88 - August 6, 2017" PNG_STRING_NEWLINE \
      "Copyright (c) 1998-2002,2004,2006-2017 Glenn Randers-Pehrson" \
      PNG_STRING_NEWLINE \
      "Copyright (c) 1996-1997 Andreas Dilger" PNG_STRING_NEWLINE \
      "Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc." \
      PNG_STRING_NEWLINE;
 #  else
-      return "libpng version 1.7.0beta88 - April 1, 2017\
+      return "libpng version 1.7.0beta88 - August 6, 2017\
       Copyright (c) 1998-2002,2004,2006-2017 Glenn Randers-Pehrson\
       Copyright (c) 1996-1997 Andreas Dilger\
       Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.";
diff --git a/png.h b/png.h
index c716291..7f3af6c 100644
--- a/png.h
+++ b/png.h
@@ -1,7 +1,7 @@
 
 /* png.h - header file for PNG reference library
  *
- * libpng version 1.7.0beta88, April 1, 2017
+ * libpng version 1.7.0beta88, August 6, 2017
  *
  * Copyright (c) 1998-2002,2004,2006-2017 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
@@ -12,7 +12,7 @@
  * Authors and maintainers:
  *   libpng versions 0.71, May 1995, through 0.88, January 1996: Guy Schalnat
  *   libpng versions 0.89, June 1996, through 0.96, May 1997: Andreas Dilger
- *   libpng versions 0.97, January 1998, through 1.7.0beta88, April 1, 2017:
+ *   libpng versions 0.97, January 1998, through 1.7.0beta88, August 6, 2017:
  *     Glenn Randers-Pehrson.
  *   See also "Contributing Authors", below.
  */
@@ -25,7 +25,7 @@
  *
  * This code is released under the libpng license.
  *
- * libpng versions 1.0.7, July 1, 2000 through 1.7.0beta88, April 1, 2017 are
+ * libpng versions 1.0.7, July 1, 2000 through 1.7.0beta88, August 6, 2017 are
  * Copyright (c) 2000-2002, 2004, 2006-2017 Glenn Randers-Pehrson, are
  * derived from libpng-1.0.6, and are distributed according to the same
  * disclaimer and license as libpng-1.0.6 with the following individuals
@@ -241,7 +241,7 @@
  * Y2K compliance in libpng:
  * =========================
  *
- *    April 1, 2017
+ *    August 6, 2017
  *
  *    Since the PNG Development group is an ad-hoc body, we can't make
  *    an official declaration.
@@ -310,7 +310,7 @@
 
 /* Version information for png.h - this should match the version in png.c */
 #define PNG_LIBPNG_VER_STRING "1.7.0beta88"
-#define PNG_HEADER_VERSION_STRING " libpng version 1.7.0beta88 - April 1, 2017\n"
+#define PNG_HEADER_VERSION_STRING " libpng version 1.7.0beta88 - August 6, 2017\n"
 
 #define PNG_LIBPNG_VER_SONUM   17
 #define PNG_LIBPNG_VER_DLLNUM  17
diff --git a/pngconf.h b/pngconf.h
index 1b1bba9..21f15fe 100644
--- a/pngconf.h
+++ b/pngconf.h
@@ -1,7 +1,7 @@
 
 /* pngconf.h - machine configurable file for libpng
  *
- * libpng version 1.7.0beta88, April 1, 2017
+ * libpng version 1.7.0beta88, August 6, 2017
  *
  * Copyright (c) 1998-2002,2004,2006-2016 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
diff --git a/projects/vstudio/README.txt b/projects/vstudio/README.txt
index 637a9c1..b3367d1 100644
--- a/projects/vstudio/README.txt
+++ b/projects/vstudio/README.txt
@@ -1,7 +1,7 @@
 
 VisualStudio instructions
 
-libpng version 1.7.0beta88 - April 1, 2017
+libpng version 1.7.0beta88 - August 6, 2017
 
 Copyright (c) 2010,2013,2015 Glenn Randers-Pehrson
 
diff --git a/projects/vstudio/zlib.props b/projects/vstudio/zlib.props
index e1a4a65..78a035c 100644
--- a/projects/vstudio/zlib.props
+++ b/projects/vstudio/zlib.props
@@ -2,7 +2,7 @@
 <!--
  * zlib.props - location of zlib source
  *
- * libpng version 1.7.0beta88 - April 1, 2017
+ * libpng version 1.7.0beta88 - August 6, 2017
  *
  * Copyright (c) 2011,2013,2014 Glenn Randers-Pehrson
  *
diff --git a/scripts/README.txt b/scripts/README.txt
index 78474f7..0350fd9 100644
--- a/scripts/README.txt
+++ b/scripts/README.txt
@@ -1,5 +1,5 @@
 
-Makefiles for  libpng version 1.7.0beta88 - April 1, 2017
+Makefiles for  libpng version 1.7.0beta88 - August 6, 2017
 
 pnglibconf.h.prebuilt       =>  Stores configuration settings
  makefile.linux    =>  Linux/ELF makefile
diff --git a/scripts/pnglibconf.h.prebuilt b/scripts/pnglibconf.h.prebuilt
index ad415c8..f948f87 100644
--- a/scripts/pnglibconf.h.prebuilt
+++ b/scripts/pnglibconf.h.prebuilt
@@ -2,7 +2,7 @@
 
 /* pnglibconf.h - library build configuration */
 
-/* libpng version 1.7.0beta88, April 1, 2017 */
+/* libpng version 1.7.0beta88, August 6, 2017 */
 
 /* Copyright (c) 1998-2016 Glenn Randers-Pehrson */