-#if !defined(HAVE_VSNPRINTF) && !defined(HAVE_C99_VSNPRINTF)
-int vsnprintf (char *str, size_t count, const char *fmt, va_list args);
+#if !defined(HAVE_VSNPRINTF) || !defined(HAVE_C99_VSNPRINTF)
+#define vsnprintf rsync_vsnprintf
+int vsnprintf(char *str, size_t count, const char *fmt, va_list args);