diff --git a/common/variables.common.subnets.tf b/common/variables.common.subnets.tf
index aa78c3d..80c8d32 100644
--- a/common/variables.common.subnets.tf
+++ b/common/variables.common.subnets.tf
@@ -10,7 +10,7 @@ variable "public_subnets" {
     tags               = map(string)
     enabled            = optional(bool, true)
     availability_zone  = optional(string)
-    availability_zones = optional(list(string))
+    availability_zones = optional(list(string), [])
     #      subnets     = list(string)
     #      labels      = list(string)
   }))
@@ -29,7 +29,7 @@ variable "private_subnets" {
     tags               = map(string)
     enabled            = optional(bool, true)
     availability_zone  = optional(string)
-    availability_zones = optional(list(string))
+    availability_zones = optional(list(string), [])
     #      subnets     = list(string)
     #      labels      = list(string)
   }))