--- a/tests/test-check-rust-format.t	Fri Nov 20 11:22:28 2020 +0100
+++ b/tests/test-check-rust-format.t	Mon Nov 23 14:33:58 2020 +0100
@@ -3,7 +3,7 @@
   $ . "$TESTDIR/helpers-testrepo.sh"
 
   $ cd "$TESTDIR"/..
-  $ RUSTFMT=$(rustup which --toolchain nightly rustfmt)
+  $ RUSTFMT=$(rustup which --toolchain nightly-2020-10-04 rustfmt)
   $ for f in `testrepohg files 'glob:**/*.rs'` ; do
   >   $RUSTFMT --check --edition=2018 --unstable-features --color=never $f
   > done