diff --git a/rust-toolchain b/rust-toolchain
new file mode 100644
index 0000000000000000000000000000000000000000..617d325ab6493134bf00a7682c89e9fe9eec7796
--- /dev/null
+++ b/rust-toolchain
@@ -0,0 +1 @@
+nightly-2017-12-21