diff --git a/sys/dev/md/md.c b/sys/dev/md/md.c
--- a/sys/dev/md/md.c
+++ b/sys/dev/md/md.c
@@ -646,6 +646,8 @@
 	case BIO_WRITE:
 	case BIO_DELETE:
 		break;
+	case BIO_FLUSH:
+		return (0);
 	default:
 		return (EOPNOTSUPP);
 	}
@@ -1026,6 +1028,8 @@
 	case BIO_WRITE:
 	case BIO_DELETE:
 		break;
+	case BIO_FLUSH:
+		return (0);
 	default:
 		return (EOPNOTSUPP);
 	}