diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9b4641d..e821e0a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Fixed
+
+- pass `--no-modify-path` to `elan-init` so installing elan no longer edits the
+  runner's persistent environment (`HKCU\Environment\PATH` on Windows,
+  `~/.profile` and friends elsewhere). `lean-action` already puts
+  `$HOME/.elan/bin` on `$GITHUB_PATH`, so this is a no-op on GitHub-hosted
+  runners; on self-hosted runners it stops every job from accumulating PATH
+  entries that outlive it
 ## v1.6.2 - 2026-10-12
 
 ### Fixed
diff --git a/scripts/install_elan.sh b/scripts/install_elan.sh
index ad678c4..f8167ca 100755
--- a/scripts/install_elan.sh
+++ b/scripts/install_elan.sh
@@ -5,8 +5,13 @@ set -e
 echo "::group::Elan Installation Output"
 
 set -o pipefail
+# `--no-modify-path` because this script puts `$HOME/.elan/bin` on `$GITHUB_PATH`
+# itself, two lines below. Without the flag elan additionally edits the user's
+# persistent environment -- `HKCU\Environment\PATH` on Windows, `~/.profile` and
+# friends elsewhere -- which is redundant on GitHub-hosted runners and outlives
+# the job on self-hosted ones.
 curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -sSf |
-  sh -s -- -y --default-toolchain none
+  sh -s -- -y --default-toolchain none --no-modify-path
 rm -f elan-init
 
 echo "$HOME/.elan/bin" >>"$GITHUB_PATH"