diff --git a/R/utils.R b/R/utils.R
index 663e11174..1166de42e 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -414,10 +414,15 @@ select_decorators <- function(decorators, scope) {
 #' @keywords internal
 normalize_decorators <- function(decorators) {
   if (checkmate::test_list(decorators, "teal_transform_module")) {
-    if (checkmate::test_names(names(decorators))) {
+    decorators_names <- names(decorators)[!names(decorators) %in% ""]
+    # Above is equivalent to decorators_names <- setdiff(names(decorators), "")
+    # but can return non-unique values. Non-unique values are checked in assert_decorators.
+    if (length(decorators_names) == 0) {
+      list(default = decorators)
+    } else if (length(decorators_names) == length(decorators)) {
       lapply(decorators, list)
     } else {
-      list(default = decorators)
+      stop("All decorators should either be named or unnamed.")
     }
   } else {
     decorators