diff --git a/INSTALL.W32 b/INSTALL.W32
index 3de6544fc5e7220d826097954266954b90ee1bef..8b22d9d05f06aa63a5227c9e43ed59319db8b41c 100644
--- a/INSTALL.W32
+++ b/INSTALL.W32
@@ -82,7 +82,8 @@
  There are various changes you can make to the Win32 compile environment. By
  default the library is not compiled with debugging symbols. If you add 'debug'
  to the mk1mf.pl lines in the do_* batch file then debugging symbols will be
- compiled in.
+ compiled in. Note that mk1mf.pl expects the platform to be the last argument
+ on the command line, so 'debug' must appear before that, as all other options.
 
  The default Win32 environment is to leave out any Windows NT specific
  features.