--- libpng-static-1.6.50.orig/configure.ac
+++ libpng-static-1.6.50/configure.ac
@@ -167,15 +167,6 @@ AC_CHECK_FUNCS([pow], ,
 AC_CHECK_FUNC([clock_gettime], , [AC_MSG_WARN([not building timepng])])
 AM_CONDITIONAL([HAVE_CLOCK_GETTIME], [test "$ac_cv_func_clock_gettime" = "yes"])
 
-AC_ARG_WITH(zlib-prefix,
-   AS_HELP_STRING([[[--with-zlib-prefix]]],
-      [prefix that may have been used in installed zlib]),
-      [ZPREFIX=${withval}],
-      [ZPREFIX='z_'])
-AC_CHECK_LIB([z], [zlibVersion], ,
-  [AC_CHECK_LIB([z], [${ZPREFIX}zlibVersion], ,
-     [AC_MSG_ERROR([zlib not installed])])])
-
 # The following is for pngvalid, to ensure it catches FP errors even on
 # platforms that don't enable FP exceptions, the function appears in the math
 # library (typically), it's not an error if it is not found.