-#if defined PATH_MAX && PATH_MAX > __BIG_BUFFER_SIZE
-# define BIG_BUFFER_SIZE PATH_MAX
-#elif defined MAXPATHLEN && MAXPATHLEN > __BIG_BUFFER_SIZE
-# define BIG_BUFFER_SIZE MAXPATHLEN
+#ifndef PATH_MAX
+/* exim.h will have ensured this exists before including us. */
+# error headers confusion, PATH_MAX missing in macros.h
+#endif
+#if (PATH_MAX*2) > __BIG_BUFFER_SIZE
+# define BIG_BUFFER_SIZE (PATH_MAX*2)