diff --git a/lib/libzfs/libzfs_pool.c b/lib/libzfs/libzfs_pool.c
index b1ddd983d..9d0366711 100644
--- a/lib/libzfs/libzfs_pool.c
+++ b/lib/libzfs/libzfs_pool.c
@@ -2753,10 +2753,11 @@ zpool_vdev_attach(zpool_handle_t *zhp,
 
 	case EDOM:
 		/*
-		 * The new device has a different alignment requirement.
+		 * The new device has a different optimal sector size.
 		 */
 		zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
-		    "devices have different sector alignment"));
+		    "new device has a different optimal sector size; use the "
+		    "option '-o ashift=N' to override the optimal size"));
 		(void) zfs_error(hdl, EZFS_BADDEV, msg);
 		break;