diff --git a/init/minio-bootstrap.sh b/init/minio-bootstrap.sh
index 2715b32..c4bc738 100644
--- a/init/minio-bootstrap.sh
+++ b/init/minio-bootstrap.sh
@@ -83,7 +83,8 @@ write_ro_prefix_policy "datacenterbingo-photos-ro" "datacenterbingo-photos" ""
 
 # Migration from asxpio-invoices/bingo/: copy whatever is missing. Remove
 # this (and the old bingo-ro policy below) once the old prefix is deleted.
-if mc ls "local/asxpio-invoices/bingo/" 2>/dev/null | grep -q .; then
+# (The mc image has no grep; test the listing with plain sh.)
+if [ -n "$(mc ls "local/asxpio-invoices/bingo/" 2>/dev/null)" ]; then
   mc mirror --quiet "local/asxpio-invoices/bingo" "local/datacenterbingo-photos/bingo"
 fi