diff --git a/runtime/doc/cmdline.txt b/runtime/doc/cmdline.txt
index d2c8196..ae364c3 100644
--- a/runtime/doc/cmdline.txt
+++ b/runtime/doc/cmdline.txt
@@ -894,7 +894,8 @@
 		directory.
 	:.	Reduce file name to be relative to current directory, if
 		possible.  File name is unmodified if it is not below the
-		current directory.
+		current directory, but on MS-Windows the drive is removed if
+		it is the current drive.
 		For maximum shortness, use ":~:.".
 	:h	Head of the file name (the last component and any separators
 		removed).  Cannot be used with :e, :r or :t.