diff --git a/README.rst b/README.rst
index dda461e44..cd43de01b 100644
--- a/README.rst
+++ b/README.rst
@@ -1,3 +1,18 @@
+``rustup`` Toolchain
+====================
+
+If you use ``rustup``, you need to configure what toolchain you want
+to use. We set the default in the file ``./rust-toolchain`` to ``system``:
+
+    # cat rust-toolchain
+    system
+
+This works if you have installed the ``rustc`` Debian packages, and told
+``rustup`` the location of that link:
+
+    # rustup toolchain link system /usr
+
+
 Versioning of proxmox helper crates
 ===================================
 
diff --git a/rust-toolchain b/rust-toolchain
index 2bf5ad044..bec3a35ee 100644
--- a/rust-toolchain
+++ b/rust-toolchain
@@ -1 +1 @@
-stable
+system