diff --git a/tests/test-git-hooks-install.sh b/tests/test-git-hooks-install.sh
index b4fd5aa..8a36350 100755
--- a/tests/test-git-hooks-install.sh
+++ b/tests/test-git-hooks-install.sh
@@ -3,6 +3,12 @@
 # Runs install.sh from a temp repo to avoid touching the real .git/hooks/.
 set -euo pipefail
 
+# This script may itself run inside a git hook (e.g. pre-push), which sets
+# GIT_DIR/GIT_EXEC_PATH/etc. in the environment. `git init`/`git -C` below
+# would silently re-target the inherited GIT_DIR instead of creating an
+# isolated repo in $TEMP_REPO, so start from a clean slate.
+for var in $(compgen -v | grep '^GIT_'); do unset "$var"; done
+
 REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 PASS=0
 FAIL=0