diff --git a/src/cluster-regional.tf b/src/cluster-regional.tf
index d24a335..f73fc2a 100644
--- a/src/cluster-regional.tf
+++ b/src/cluster-regional.tf
@@ -34,7 +34,7 @@ module "aurora_postgres_cluster" {
   storage_encrypted                    = var.storage_encrypted
   storage_type                         = var.storage_type
   kms_key_arn                          = var.storage_encrypted ? module.kms_key_rds.key_arn : null
-  performance_insights_kms_key_id      = var.performance_insights_enabled ? module.kms_key_rds.key_arn : null
+  performance_insights_kms_key_id      = var.performance_insights_enabled ? coalesce(var.performance_insights_kms_key_arn, module.kms_key_rds.key_arn) : null
   maintenance_window                   = var.maintenance_window
   enabled_cloudwatch_logs_exports      = var.enabled_cloudwatch_logs_exports
   enhanced_monitoring_role_enabled     = var.enhanced_monitoring_role_enabled
diff --git a/src/variables.tf b/src/variables.tf
index 92d9f4b..c8649f4 100644
--- a/src/variables.tf
+++ b/src/variables.tf
@@ -200,6 +200,12 @@ variable "performance_insights_enabled" {
   description = "Whether to enable Performance Insights"
 }
 
+variable "performance_insights_kms_key_arn" {
+  type        = string
+  default     = null
+  description = "ARN of the KMS key for Performance Insights encryption. If null, defaults to the RDS CMK."
+}
+
 variable "database_insights_mode" {
   type        = string
   description = "The database insights mode for the RDS cluster. Valid values are `standard`, `advanced`. See https://registry.terraform.io/providers/hashicorp/aws/6.16.0/docs/resources/rds_cluster#database_insights_mode-1"