diff --git a/infra/activate_release.sh b/infra/activate_release.sh
index ceb1b190..828e1cb5 100755
--- a/infra/activate_release.sh
+++ b/infra/activate_release.sh
@@ -10,24 +10,31 @@ if [[ ! "${1:-}" =~ ^[0-9a-f]{40}$ ]]; then
   exit 64
 fi
 
+# deploy.sh uploads into a private per-deploy directory; /tmp is the older layout.
+upload_dir="${TIN_LITE_UPLOAD_DIR:-/tmp}"
+if [[ "${upload_dir}" != /tmp && ! "${upload_dir}" =~ ^/tmp/tin-deploy\.[A-Za-z0-9]{10}$ ]]; then
+  echo "TIN_LITE_UPLOAD_DIR must be /tmp or a deploy directory under it" >&2
+  exit 64
+fi
+
 cleanup() {
-  rm -f /tmp/tin-lite-github-app.pem
+  rm -f "${upload_dir}/tin-lite-github-app.pem"
 }
 trap cleanup EXIT
 
 release_sha="$1"
 release_dir="/opt/tin-lite/releases/${release_sha}"
 install -d -m 750 -o tinlite -g tinlite "${release_dir}"
-tar -xzf /tmp/tin-lite-release.tar.gz -C "${release_dir}"
-if [[ -f /tmp/tin-lite-github-app.pem ]]; then
+tar -xzf "${upload_dir}/tin-lite-release.tar.gz" -C "${release_dir}"
+if [[ -f "${upload_dir}/tin-lite-github-app.pem" ]]; then
   install -m 640 -o root -g tinlite \
-    /tmp/tin-lite-github-app.pem /etc/tin-lite/github-app.pem
+    "${upload_dir}/tin-lite-github-app.pem" /etc/tin-lite/github-app.pem
   sed -i \
     's#^TIN_LITE_GITHUB_APP_PRIVATE_KEY_PATH=.*#TIN_LITE_GITHUB_APP_PRIVATE_KEY_PATH=/etc/tin-lite/github-app.pem#' \
-    /tmp/tin-lite.env
+    "${upload_dir}/tin-lite.env"
 fi
 # An uploaded .env wins; otherwise the release env kept on the host (staging) is used.
-release_env=/tmp/tin-lite.env
+release_env="${upload_dir}/tin-lite.env"
 if [[ ! -f "${release_env}" ]]; then
   release_env=/etc/tin-lite/release.env
 fi
@@ -53,4 +60,4 @@ ln -sfn "${release_dir}" /opt/tin-lite/current
 systemctl enable tin-lite-switchboard
 systemctl restart tin-lite-switchboard
 
-rm -f /tmp/tin-lite-release.tar.gz /tmp/tin-lite.env
+rm -f "${upload_dir}/tin-lite-release.tar.gz" "${upload_dir}/tin-lite.env"
diff --git a/infra/deploy.sh b/infra/deploy.sh
index 6738f27f..9f157a49 100755
--- a/infra/deploy.sh
+++ b/infra/deploy.sh
@@ -66,6 +66,16 @@ temporary_dir="$(mktemp -d)"
 trap 'rm -rf "${temporary_dir}"' EXIT
 git archive --format=tar.gz --output="${temporary_dir}/tin-lite-release.tar.gz" HEAD
 
+# Each deploy uploads into its own private directory, so deploys by different people (or
+# by CI) never collide on files another account left in /tmp.
+upload_dir="$(gcloud compute ssh "${instance}" \
+  --project "${TIN_LITE_GCP_PROJECT}" --zone "${zone}" --quiet \
+  --command='mktemp -d /tmp/tin-deploy.XXXXXXXXXX' | tr -d '\r')"
+if [[ ! "${upload_dir}" =~ ^/tmp/tin-deploy\.[A-Za-z0-9]{10}$ ]]; then
+  echo "could not create a private upload directory on ${instance}" >&2
+  exit 70
+fi
+
 release_files=("${temporary_dir}/tin-lite-release.tar.gz")
 if [[ "${upload_env}" == "1" ]]; then
   release_files+=(.env)
@@ -77,18 +87,18 @@ gcloud compute scp \
   infra/proxy_policy.py \
   src/tin_lite/proxy_grants.py \
   infra/activate_release.sh \
-  "${instance}:/tmp/" \
+  "${instance}:${upload_dir}/" \
   --project "${TIN_LITE_GCP_PROJECT}" --zone "${zone}" --quiet
 
 if [[ -n "${github_private_key_path}" ]]; then
   gcloud compute scp \
     "${github_private_key_path}" \
-    "${instance}:/tmp/tin-lite-github-app.pem" \
+    "${instance}:${upload_dir}/tin-lite-github-app.pem" \
     --project "${TIN_LITE_GCP_PROJECT}" --zone "${zone}" --quiet
   gcloud compute ssh "${instance}" \
     --project "${TIN_LITE_GCP_PROJECT}" --zone "${zone}" --quiet \
-    --command="sudo chown root:root /tmp/tin-lite-github-app.pem && \
-sudo chmod 600 /tmp/tin-lite-github-app.pem"
+    --command="sudo chown root:root ${upload_dir}/tin-lite-github-app.pem && \
+sudo chmod 600 ${upload_dir}/tin-lite-github-app.pem"
 fi
 
 static_ip="${TIN_LITE_STATIC_IP:-}"
@@ -107,12 +117,13 @@ if [[ ! "${product_host}" =~ ^[a-zA-Z0-9.-]+$ ]]; then
 fi
 move_env=""
 if [[ "${upload_env}" == "1" ]]; then
-  move_env="sudo mv /tmp/.env /tmp/tin-lite.env && "
+  move_env="mv ${upload_dir}/.env ${upload_dir}/tin-lite.env && "
 fi
 gcloud compute ssh "${instance}" \
   --project "${TIN_LITE_GCP_PROJECT}" --zone "${zone}" --quiet \
-  --command="sudo env TIN_LITE_STATIC_IP=${static_ip} TIN_LITE_PRODUCT_HOST=${product_host} bash /tmp/install_switchboard.sh && \
-${move_env}sudo env TIN_LITE_RUN_MIGRATIONS=${run_migrations} bash /tmp/activate_release.sh ${release_sha}"
+  --command="sudo env TIN_LITE_STATIC_IP=${static_ip} TIN_LITE_PRODUCT_HOST=${product_host} bash ${upload_dir}/install_switchboard.sh && \
+${move_env}sudo env TIN_LITE_UPLOAD_DIR=${upload_dir} TIN_LITE_RUN_MIGRATIONS=${run_migrations} bash ${upload_dir}/activate_release.sh ${release_sha}; \
+status=\$?; sudo rm -rf ${upload_dir}; exit \$status"
 
 public_host="tin-lite-switchboard.${static_ip//./-}.sslip.io"
 curl --http1.1 --fail --silent --show-error --retry "${health_retries}" --retry-all-errors --retry-delay 3 \
diff --git a/tests/test_secret_fences.py b/tests/test_secret_fences.py
index 91b1660a..c53543c7 100644
--- a/tests/test_secret_fences.py
+++ b/tests/test_secret_fences.py
@@ -52,8 +52,10 @@ def test_github_private_key_is_installed_as_host_state_not_release_state() -> No
     activate = (ROOT / "infra" / "activate_release.sh").read_text()
 
     assert 'openssl pkey -in "${github_private_key_path}" -check -noout' in deploy
-    assert '"${instance}:/tmp/tin-lite-github-app.pem"' in deploy
-    assert "sudo chmod 600 /tmp/tin-lite-github-app.pem" in deploy
+    assert '"${instance}:${upload_dir}/tin-lite-github-app.pem"' in deploy
+    assert "sudo chmod 600 ${upload_dir}/tin-lite-github-app.pem" in deploy
+    assert "mktemp -d /tmp/tin-deploy.XXXXXXXXXX" in deploy
+    assert "sudo rm -rf ${upload_dir}" in deploy
     assert "install -m 640 -o root -g tinlite" in activate
     assert "/etc/tin-lite/github-app.pem" in activate
     assert "TIN_LITE_GITHUB_APP_PRIVATE_KEY_PATH=/etc/tin-lite/github-app.pem" in activate