diff --git a/hooks/pre-exit b/hooks/pre-exit
index e2fc038..41233ae 100755
--- a/hooks/pre-exit
+++ b/hooks/pre-exit
@@ -2,7 +2,7 @@
 
 set -euo pipefail
 
-if [[ -v BUILDKITE_OIDC_TMPDIR ]]; then
+if [[ -n "${BUILDKITE_OIDC_TMPDIR:-}" ]]; then
   rm -rf "$BUILDKITE_OIDC_TMPDIR"
 
   echo "Removed credentials from $BUILDKITE_OIDC_TMPDIR"