diff -aprNU5 zlib-1.2.3.orig/zutil.h zlib-1.2.3/zutil.h
--- zlib-1.2.3.orig/zutil.h	2005-07-11 20:35:48 +0000
+++ zlib-1.2.3/zutil.h	2006-04-30 19:55:30 +0000
@@ -183,11 +183,11 @@ extern const char * const z_errmsg[10]; 
 #if defined(__CYGWIN__)
 #  ifndef HAVE_VSNPRINTF
 #    define HAVE_VSNPRINTF
 #  endif
 #endif
-#ifndef HAVE_VSNPRINTF
+#if !defined(HAVE_VSNPRINTF) && !defined(NO_vsnprintf)
 #  ifdef MSDOS
      /* vsnprintf may exist on some MS-DOS compilers (DJGPP?),
         but for now we just assume it doesn't. */
 #    define NO_vsnprintf
 #  endif
