diff --git a/rust-toolchain b/rust-toolchain
new file mode 100644
index 0000000..d4e1e1f
--- /dev/null
+++ b/rust-toolchain
@@ -0,0 +1,9 @@
+# If you see this, run `rustup self update` to get rustup 1.23 or newer.
+
+# NOTE: above comment is for older `rustup` (before TOML support was added),
+# which will treat the first line as the toolchain name, and therefore show it
+# to the user in the error, instead of "error: invalid channel name '[toolchain]'".
+
+[toolchain]
+channel = "nightly-2021-08-27"
+components = ["rust-src", "rustc-dev", "llvm-tools-preview"]