diff --git a/variables.tf b/variables.tf
index d563ca9..e915fbf 100644
--- a/variables.tf
+++ b/variables.tf
@@ -257,9 +257,10 @@ variable "archive_on_destroy" {
 }
 
 variable "vulnerability_alerts" {
-  description = "Enable Dependabot alerts"
+  description = "Enable Dependabot alerts. Defaults to null (unmanaged) to avoid calling the\nvulnerability-alerts API endpoint, which returns 404 on GitHub Enterprise Server 3.x."
   type        = bool
-  default     = false
+  nullable    = true
+  default     = null
 }
 
 variable "gitignore_template" {