diff --git a/lib/libzfs/libzfs_pool.c b/lib/libzfs/libzfs_pool.c
index 8a043aa0f..e493e8562 100644
--- a/lib/libzfs/libzfs_pool.c
+++ b/lib/libzfs/libzfs_pool.c
@@ -3733,6 +3733,13 @@ zpool_vdev_attach(zpool_handle_t *zhp, const char *old_disk,
 			(void) zpool_standard_error(hdl, errno, errbuf);
 		}
 		break;
+
+	case ZFS_ERR_ASHIFT_MISMATCH:
+		zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
+		    "The new device cannot have a higher alignment requirement "
+		    "than the top-level vdev."));
+		(void) zfs_error(hdl, EZFS_BADTARGET, errbuf);
+		break;
 	default:
 		(void) zpool_standard_error(hdl, errno, errbuf);
 	}
diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index cafc7196c..99a8d107e 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -7602,8 +7602,10 @@ spa_vdev_attach(spa_t *spa, uint64_t guid, nvlist_t *nvroot, int replacing,
 	 * The new device cannot have a higher alignment requirement
 	 * than the top-level vdev.
 	 */
-	if (newvd->vdev_ashift > oldvd->vdev_top->vdev_ashift)
-		return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
+	if (newvd->vdev_ashift > oldvd->vdev_top->vdev_ashift) {
+		return (spa_vdev_exit(spa, newrootvd, txg,
+		    ZFS_ERR_ASHIFT_MISMATCH));
+	}
 
 	/*
 	 * RAIDZ-expansion-specific checks.