diff --git a/NAMESPACE b/NAMESPACE
index 8a2747a..3109ab4 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -20,3 +20,4 @@ export(slope_z_mean)
 export(slope_z_min)
 export(slope_z_start)
 export(slope_z_value)
+importFrom(methods,is)
diff --git a/R/slopes.R b/R/slopes.R
index 5398fd5..107aebb 100644
--- a/R/slopes.R
+++ b/R/slopes.R
@@ -143,6 +143,7 @@ slope_matrices = function(m_xyz_split, fun = slope_matrix_weighted, ...) {
 #'   datasets. Default: `"bilinear"`.
 #' @param fun The slope function to calculate per route,
 #'   `slope_matrix_weighted` by default.
+#' @importFrom methods is
 #' @export
 #' @examples
 #' r = lisbon_road_segments[1:3, ]