diff --git a/migrations/006-install-postgres.sh b/migrations/006-install-postgres.sh
index 7f9bea0..a7fb7bc 100644
--- a/migrations/006-install-postgres.sh
+++ b/migrations/006-install-postgres.sh
@@ -22,7 +22,7 @@ case "${1:-}" in
     systemctl enable --now postgresql >/dev/null
     pg_isready -q
     pg_lsclusters --no-header | while read -r _ _ _ _ _ datadir _; do
-      if findmnt -rn "$datadir" >/dev/null; then
+      if [[ $(findmnt -rn -o TARGET -T "$datadir") == "$PGROOT" ]]; then
         echo "    cluster data on dedicated disk: $datadir"
       else
         echo "    WARNING: $datadir is NOT on the dedicated disk" >&2