diff --git a/README.md b/README.md
index d87b12f..c0e5c89 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,13 @@ Copyright ©2020–2022 Tony Garnock-Jones.
 SqueakPhone comes in two pieces: this is the `git`-based portion, and **there's another part
 that lives in [SqueakSource](https://squeaksource.com/SqueakPhone.html)**.
 
+## Setting up your local Unix account
+
+The `LinuxIO` package depends on being able to access `/dev/input/*`, which means on Debian at
+least that your user needs to be in the `input` group. This applies not only for running the
+image, but for *building* it too, even if you don't plan to develop with it on your local build
+host.
+
 ## Loading the Smalltalk code into an existing image
 
 You can work with most of the codebase without actually running it on a phone. (In fact, it