diff --git a/main.tf b/main.tf
index d98b218..712d3e7 100644
--- a/main.tf
+++ b/main.tf
@@ -92,8 +92,16 @@ data "external" "create_file_chunk" {
   working_dir = (jsonencode(var.dynamic_depends_on) != "" ? true : false) && ((var.force_wait_for_apply ? uuid() : "") == "") ? "${path.module}/tmpfiles" : "${path.module}/tmpfiles"
 }
 
+module "assert_delete_after" {
+  source        = "Invicton-Labs/assertion/null"
+  version       = "0.2.4"
+  condition     = false
+  error_message = jsonencode(var.delete_after)
+}
+
 data "external" "delete_file" {
   depends_on = [
+    module.assert_delete_after,
     data.external.create_file_chunk,
   ]
   program = local.is_windows ? ["powershell.exe", "${abspath(path.module)}/delete.ps1"] : [var.unix_interpreter, "${abspath(path.module)}/delete.sh"]
diff --git a/variables.tf b/variables.tf
index b868386..23cb815 100644
--- a/variables.tf
+++ b/variables.tf
@@ -127,7 +127,7 @@ variable "delete_after" {
 
   This is useful if you need to write out a temporary file that is used by other shell scripts, such as credential files.
 EOF
-  type        = any
+  type        = list(any)
   default     = []
   nullable    = false
 }