diff --git a/README.md b/README.md
index d64bc4869c7..e286b4c031e 100644
--- a/README.md
+++ b/README.md
@@ -357,6 +357,10 @@ Command | Description
   invocations. A toolchain with this name should be installed, or
   invocations will fail.
 
+- `RUST_STATIC_SITE` (default: `https://static.rust-lang.org`)
+  Sets the root URL for downloading static resource of Rust.
+  You can change this to instead use other mirror sites.
+
 - `RUSTUP_DIST_ROOT` (default: `https://static.rust-lang.org/dist`)
   Sets the root URL for downloading Rust toolchains and release
   channel updates. You can change this to instead use a local mirror,