diff --git a/routing/main.tf b/routing/main.tf
index 2dc4cd4..3d9eb1d 100644
--- a/routing/main.tf
+++ b/routing/main.tf
@@ -44,7 +44,7 @@ locals {
 # route table: public
 #---
 resource "aws_route_table" "public" {
-  for_each = var.create_public_route_table ? local.availability_zones : {}
+  for_each = var.create_public_route_table ? local.availability_zones : toset([])
   vpc_id   = var.vpc_id
 
   tags = merge(
@@ -64,7 +64,7 @@ resource "aws_route_table_association" "public" {
 # route table: private
 #---
 resource "aws_route_table" "private" {
-  for_each = var.create_private_route_table ? local.availability_zones : {}
+  for_each = var.create_private_route_table ? local.availability_zones : toset([])
   vpc_id   = var.vpc_id
 
   tags = merge(
@@ -87,7 +87,7 @@ resource "aws_route_table_association" "private" {
 #   NATGW
 #---
 resource "aws_eip" "nat" {
-  for_each = var.enable_igw && var.enable_nat ? local.availability_zones : {}
+  for_each = var.enable_igw && var.enable_nat ? local.availability_zones : toset([])
   vpc      = true
 
   tags = merge(
@@ -131,14 +131,14 @@ resource "aws_nat_gateway" "nat" {
 }
 
 resource "aws_route" "nat_public" {
-  for_each               = var.create_public_route_table && var.enable_igw && var.enable_nat ? local.availability_zones : {}
+  for_each               = var.create_public_route_table && var.enable_igw && var.enable_nat ? local.availability_zones : toset([])
   route_table_id         = aws_route_table.public[each.key].id
   destination_cidr_block = "0.0.0.0/0"
   gateway_id             = aws_internet_gateway.gateway[0].id
 }
 
 resource "aws_route" "nat_private" {
-  for_each               = var.create_private_route_table && var.enable_igw && var.enable_nat ? local.availability_zones : {}
+  for_each               = var.create_private_route_table && var.enable_igw && var.enable_nat ? local.availability_zones : toset([])
   route_table_id         = aws_route_table.private[each.key].id
   destination_cidr_block = "0.0.0.0/0"
   nat_gateway_id         = aws_nat_gateway.nat[each.key].id