diff --git a/ANNOUNCE b/ANNOUNCE
index 6041d1529..9788b6f4b 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -29,6 +29,8 @@ Changes since the last public release (1.6.13):
 Version 1.6.13beta01 [June 13, 2014]
   Quieted -Wsign-compare and -Wclobber compiler warnings in
     contrib/pngminus/*.c
+  Added "(void) png_ptr;" where needed in contrib/gregbook to quiet
+    compiler complaints about unused pointers.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
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diff --git a/CHANGES b/CHANGES
index 3d169d969..fac56b53b 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4943,6 +4943,8 @@ Version 1.6.12 [June 12, 2014]
 Version 1.6.13beta01 [June 13, 2014]
   Quieted -Wsign-compare and -Wclobber compiler warnings in
     contrib/pngminus/*.c
+  Added "(void) png_ptr;" where needed in contrib/gregbook to quiet
+    compiler complaints about unused pointers.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/contrib/gregbook/readpng2.c b/contrib/gregbook/readpng2.c
index e6a132eca..4150fa4d8 100644
--- a/contrib/gregbook/readpng2.c
+++ b/contrib/gregbook/readpng2.c
@@ -448,6 +448,8 @@ static void readpng2_end_callback(png_structp png_ptr, png_infop info_ptr)
 
     /* all done */
 
+    (void)info_ptr; /* Unused */
+
     return;
 }
 
@@ -472,6 +474,8 @@ static void readpng2_warning_handler(png_structp png_ptr, png_const_charp msg)
 {
     fprintf(stderr, "readpng2 libpng warning: %s\n", msg);
     fflush(stderr);
+    PNG_UNUSED(png_ptr)
+    (void)png_ptr; /* Unused */
 }