diff --git a/R/zzz.R b/R/zzz.R
index 3b06ca8..34b95e7 100644
--- a/R/zzz.R
+++ b/R/zzz.R
@@ -174,7 +174,7 @@ rvc <- function(x) Filter(Negate(is.null), x)
 
 assert <- function(x, y) {
   if (!is.null(x)) {
-    if (!class(x) %in% y) {
+    if (!inherits(x, y)) {
       stop(deparse(substitute(x)), " must be of class ",
            paste0(y, collapse = ", "), call. = FALSE)
     }