diff --git a/custom/custom.tf b/custom/custom.tf
index 1eed1d4..c1c2d7e 100644
--- a/custom/custom.tf
+++ b/custom/custom.tf
@@ -123,7 +123,7 @@ resource "aws_security_group" "this_security_group" {
 
   # inress with prefix lists
   dynamic "ingress" {
-    for_each = length(var.ingress_prefix_list_names) && length(var.ingress_prefix_list_ports) > 0 ? toset(var.ingress_prefix_list_ports) : toset([])
+    for_each = length(var.ingress_prefix_list_names) > 0 && length(var.ingress_prefix_list_ports) > 0 ? toset(var.ingress_prefix_list_ports) : toset([])
     iterator = p
     content {
       description     = try(p.value.label, local.short_description)
@@ -162,7 +162,7 @@ resource "aws_security_group" "this_security_group" {
 
   # egress with prefix lists
   dynamic "egress" {
-    for_each = length(var.egress_prefix_list_names) && length(var.egress_prefix_list_ports) > 0 ? toset(var.egress_prefix_list_ports) : toset([])
+    for_each = length(var.egress_prefix_list_names) > 0 && length(var.egress_prefix_list_ports) > 0 ? toset(var.egress_prefix_list_ports) : toset([])
     iterator = p
     content {
       description     = try(p.value.label, local.short_description)