diff --git a/README b/README
index 83f6ad9..df561e2 100644
--- a/README
+++ b/README
@@ -136,3 +136,20 @@ version to release, and the second the output directory. This will
 create a source tarball, a documentation tarball if a doxygen module is
 detected, and will also attempt to sign the tarballs with gpg (although
 it is not a fatal error if this step fails).
+
+Upgrading build system
+----------------------
+
+Sometimes, the nonvolatile parts of the build system (the static parts
+that are committed to the repository) need to be upgraded as well. There
+is a script to do this in the lw-build-system repository.
+
+From the project base directory, run the script 
+`/path/to/lw-build-system/update.sh'. This only works if symlinks are
+installed. It will create a patch file, which you should edit before
+applying.
+
+Unfortunately, the upgrade process is not perfect and will not detect
+legitimate changes you have made to files such as `config' and modules'
+`build.*' files. You will need to manually edit the patch to revert
+false positives.