diff --git a/winsup/doc/install.texinfo b/winsup/doc/install.texinfo
index 10a401f4b..f3889f9e8 100644
--- a/winsup/doc/install.texinfo
+++ b/winsup/doc/install.texinfo
@@ -178,6 +178,36 @@ without spaces.
 /etc/passwd, you may need to make corresponding changes there.  See the
 README file for that package.)
 
+@subsection Setup screwed up my mounts!
+
+Setup will remove the following mounts, should you have them:
+
+@example
+	/
+        /usr
+        /usr/bin
+        /usr/lib
+        /var
+        /lib
+        /bin
+        /etc
+@end example
+
+It will then restore (or create new) mounts for /, /usr/bin and /usr/lib
+as follows (assuming the default install root C:\cygwin):
+
+@example
+	Device              Directory
+	C:\cygwin\bin       /usr/bin
+	C:\cygwin\lib       /usr/lib
+	C:\cygwin           /
+@end example
+
+Since setup is not a Cygwin program, it cannot know about your mounts
+(or symlinks, for that matter), and so must impose and enforce this
+structure.  You should not try to defeat it, unless you know what you
+are doing and can deal with the consequences.
+
 @subsection How do I uninstall Cygwin?
 
 Setup has no automatic uninstall facility.  Just delete everything