Rustup not installed at [location] with different CARGO_HOME and RUSTUP_HOME

Verification

• I searched for recent similar issues at https://github.com/rust-lang/rustup/issues?q=is%3Aissue and found no duplicates.
• I am on the latest version of Rustup according to https://github.com/rust-lang/rustup/tags and am still able to reproduce my issue.

Problem

Running rustup update does update the version but ends with error: rustup is not installed at [location of $RUSTUP_HOME].

I did check the RUSTUP_HOME and CARGO_HOME. They are set as follows:

• $RUSTUP_HOME: custom/location/rustup/bin
• $CARGO_HOME: custom/location/cargo/bin

Both are sitting at the same custom/location just with different suffices.

I did check the actual location and the error message is correct. The rustup binary itself is installed at $CARGO_HOME/rustup together with all the other binaries such as cargo, rust-analyzer and more.

In the $RUSTUP_HOME are the installed toolchains, but no binaries.

Steps

1. Install rustup via rust installer (curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh)
2. run rustup update
3. Rustup update works but ends with error

Possible Solution(s)

No response

Notes

No response

Rustup version

rustup 1.29.0 (28d1352db 2026-03-05)
info: This is the version for the rustup toolchain manager, not the rustc compiler.
info: the currently active `rustc` version is `rustc 1.96.0 (ac68faa20 2026-05-25)`

Installed toolchains

Default host: aarch64-apple-darwin
rustup home:  [redacted]

installed toolchains
--------------------
stable-aarch64-apple-darwin (active, default)

active toolchain
----------------
name: stable-aarch64-apple-darwin
active because: it's the default toolchain
installed targets:
  aarch64-apple-darwin

OS version

macOS 26.5.1 on Apple Silicon Chip

Start by reproducing the issue with different RUSTUP_HOME and CARGO_HOME values, using the documented rustup installer and rustup update steps. Trace how the update command determines the rustup installation location, then verify that an update completes without the incorrect installation-location error.