diff --git a/libc/upstream-freebsd/README.txt b/libc/upstream-freebsd/README.txt
new file mode 100644
index 0000000..fbfc04a
--- /dev/null
+++ b/libc/upstream-freebsd/README.txt
@@ -0,0 +1,5 @@
+This directory contains upstream FreeBSD source. You should not edit these
+files directly. Make fixes upstream and then pull down the new version of
+the file.
+
+TODO: write a script to make this process automated.