diff --git a/infrastructure/terraform/lambda/_template/variables.tf b/infrastructure/terraform/lambda/_template/variables.tf
index ae588840..c4408e0f 100644
--- a/infrastructure/terraform/lambda/_template/variables.tf
+++ b/infrastructure/terraform/lambda/_template/variables.tf
@@ -19,7 +19,7 @@ variable "image_digest" {
 
 variable "maximum_concurrency" {
   type        = number
-  default     = null
+  default     = 1
   description = "Maximum number of concurrent Lambda invocations from SQS (2-1000). null = no limit."
 }
 
diff --git a/infrastructure/terraform/lambda/hubspot_deal_etl/variables.tf b/infrastructure/terraform/lambda/hubspot_deal_etl/variables.tf
index 285b6a4c..27c9424b 100644
--- a/infrastructure/terraform/lambda/hubspot_deal_etl/variables.tf
+++ b/infrastructure/terraform/lambda/hubspot_deal_etl/variables.tf
@@ -19,13 +19,13 @@ variable "image_digest" {
 
 variable "maximum_concurrency" {
   type        = number
-  default     = null
+  default     = 1
   description = "Maximum number of concurrent Lambda invocations from SQS (2-1000). null = no limit."
 }
 
 variable "batch_size" {
   type    = number
-  default = 1
+  default = 10
 }
 
 locals {
diff --git a/infrastructure/terraform/lambda/ordnanceSurvey/variables.tf b/infrastructure/terraform/lambda/ordnanceSurvey/variables.tf
index 936aebc9..e2cfd65e 100644
--- a/infrastructure/terraform/lambda/ordnanceSurvey/variables.tf
+++ b/infrastructure/terraform/lambda/ordnanceSurvey/variables.tf
@@ -19,7 +19,7 @@ variable "image_digest" {
 
 variable "maximum_concurrency" {
   type        = number
-  default     = null
+  default     = 1
   description = "Maximum number of concurrent Lambda invocations from SQS (2-1000). null = no limit."
 }
 
diff --git a/infrastructure/terraform/lambda/pashub_to_ara/variables.tf b/infrastructure/terraform/lambda/pashub_to_ara/variables.tf
index e7646811..fe92d645 100644
--- a/infrastructure/terraform/lambda/pashub_to_ara/variables.tf
+++ b/infrastructure/terraform/lambda/pashub_to_ara/variables.tf
@@ -19,7 +19,7 @@ variable "image_digest" {
 
 variable "maximum_concurrency" {
   type        = number
-  default     = null
+  default     = 1
   description = "Maximum number of concurrent Lambda invocations from SQS (2-1000). null = no limit."
 }
 
diff --git a/infrastructure/terraform/modules/lambda_sqs_trigger/variables.tf b/infrastructure/terraform/modules/lambda_sqs_trigger/variables.tf
index c3127c74..0b8dffc0 100644
--- a/infrastructure/terraform/modules/lambda_sqs_trigger/variables.tf
+++ b/infrastructure/terraform/modules/lambda_sqs_trigger/variables.tf
@@ -9,6 +9,6 @@ variable "batch_size" {
 
 variable "maximum_concurrency" {
   type        = number
-  default     = null
+  default     = 1
   description = "Maximum number of concurrent Lambda invocations from SQS. null = no limit."
 }
diff --git a/infrastructure/terraform/modules/lambda_with_sqs/variables.tf b/infrastructure/terraform/modules/lambda_with_sqs/variables.tf
index 7c2832d2..6d992f3b 100644
--- a/infrastructure/terraform/modules/lambda_with_sqs/variables.tf
+++ b/infrastructure/terraform/modules/lambda_with_sqs/variables.tf
@@ -37,6 +37,6 @@ variable "batch_size" {
 
 variable "maximum_concurrency" {
   type        = number
-  default     = null
+  default     = 1
   description = "Maximum number of concurrent Lambda invocations from SQS. null = no limit."
 }