diff --git a/.Rbuildignore b/.Rbuildignore
index 2ef8ba9063900318c7c0be04cc2ac48a636842e4..d0a3f0a66a799dbbad8e84e6f8503e89a766c215 100644
--- a/.Rbuildignore
+++ b/.Rbuildignore
@@ -9,7 +9,7 @@
 ^inst/doc$
 ^\.gitlab-ci\.yml$
 ## unit tests should be ignored when building the package for CRAN
-^tests$
+#^tests$
 ^inst/PlotProfiling\.R$
 
 # Suggested by http://r-pkgs.had.co.nz/package.html
diff --git a/R/Start.R b/R/Start.R
index 1251634b83286f0cabc6af45dffe63c14ea05019..c5a0a4c9dd8ca4dceb22b3c0164590c77d27e7a7 100644
--- a/R/Start.R
+++ b/R/Start.R
@@ -1385,7 +1385,7 @@ Start <- function(..., # dim = indices/selectors,
       # names as depended dim.
       for (j in 1:length(dat_selectors[[file_dim]])) {
         sv <- selector_vector <- dat_selectors[[file_dim]][[j]]
-        if (!is(sv, first_class) ||
+        if (!inherits(sv, first_class) ||
             !identical(first_length, length(sv))) {
           stop("All provided selectors for depending dimensions must ",
                "be vectors of the same length and of the same class.")
@@ -3967,7 +3967,7 @@ Start <- function(..., # dim = indices/selectors,
         if (!identical(inner_dim_has_split_dim, character(0))) {
           metadata_tmp <- array(picked_common_vars[[inner_dim_has_split_dim]], dim = final_dims_fake_metadata)
           # Convert numeric back to dates
-          if (is(picked_common_vars[[inner_dim_has_split_dim]], 'POSIXct')) {
+          if (inherits(picked_common_vars[[inner_dim_has_split_dim]], 'POSIXct')) {
             metadata_tmp <- as.POSIXct(metadata_tmp, origin = "1970-01-01", tz = 'UTC')
           }
           picked_common_vars[[inner_dim_has_split_dim]] <- metadata_tmp
@@ -4096,7 +4096,7 @@ Start <- function(..., # dim = indices/selectors,
         if (!identical(inner_dim_has_split_dim, character(0))) {
           metadata_tmp <- array(picked_common_vars[[inner_dim_has_split_dim]], dim = final_dims_fake_metadata)
           # Convert numeric back to dates
-          if (is(picked_common_vars[[inner_dim_has_split_dim]], 'POSIXct')) {
+          if (inherits(picked_common_vars[[inner_dim_has_split_dim]], 'POSIXct')) {
             metadata_tmp <- as.POSIXct(metadata_tmp, origin = "1970-01-01", tz = 'UTC')
           }
           picked_common_vars[[inner_dim_has_split_dim]] <- metadata_tmp