diff --git a/src/buffer.h b/src/buffer.h
index d456e1bd68e..2889d263820 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -272,10 +272,10 @@ struct buffer
     Lisp_Object left_margin;
     /* Function to call when insert space past fill column */
     Lisp_Object auto_fill_function;
-#ifdef MSDOS
+#ifdef DOS_NT
     /* nil: text, t: binary.  */
     Lisp_Object buffer_file_type;
-#endif
+#endif /* DOS_NT */
 
     /* String of length 256 mapping each char to its lower-case version.  */
     Lisp_Object downcase_table;