diff --git a/templates/xcode.pkr.hcl b/templates/xcode.pkr.hcl
index 6dafd9b..b050efd 100644
--- a/templates/xcode.pkr.hcl
+++ b/templates/xcode.pkr.hcl
@@ -17,6 +17,7 @@ variable "xcode_version" {
 
 variable "additional_runtimes" {
   type = list(string)
+  default = []
 }
 
 variable "tag" {