diff --git a/modules/runners/variables.tf b/modules/runners/variables.tf
index 75e851695e..252cac305e 100644
--- a/modules/runners/variables.tf
+++ b/modules/runners/variables.tf
@@ -58,26 +58,18 @@ variable "s3_runner_binaries" {
 variable "block_device_mappings" {
   description = "The EC2 instance block device configuration. Takes the following keys: `device_name`, `delete_on_termination`, `volume_type`, `volume_size`, `encrypted`, `iops`, `throughput`, `kms_key_id`, `snapshot_id`."
   type = list(object({
-    delete_on_termination = bool
-    device_name           = string
-    encrypted             = bool
-    iops                  = number
-    kms_key_id            = string
-    snapshot_id           = string
-    throughput            = number
+    delete_on_termination = optional(bool, true)
+    device_name           = optional(string, "/dev/xvda")
+    encrypted             = optional(bool, true)
+    iops                  = optional(number)
+    kms_key_id            = optional(string)
+    snapshot_id           = optional(string)
+    throughput            = optional(number)
     volume_size           = number
-    volume_type           = string
+    volume_type           = optional(string, "gp3")
   }))
   default = [{
-    delete_on_termination = true
-    device_name           = "/dev/xvda"
-    encrypted             = true
-    iops                  = null
-    kms_key_id            = null
-    snapshot_id           = null
-    throughput            = null
-    volume_size           = 30
-    volume_type           = "gp3"
+    volume_size = 30
   }]
 }
 
diff --git a/variables.tf b/variables.tf
index eaf0651740..d69f952331 100644
--- a/variables.tf
+++ b/variables.tf
@@ -274,26 +274,18 @@ variable "runner_allow_prerelease_binaries" {
 variable "block_device_mappings" {
   description = "The EC2 instance block device configuration. Takes the following keys: `device_name`, `delete_on_termination`, `volume_type`, `volume_size`, `encrypted`, `iops`, `throughput`, `kms_key_id`, `snapshot_id`."
   type = list(object({
-    delete_on_termination = bool
-    device_name           = string
-    encrypted             = bool
-    iops                  = number
-    kms_key_id            = string
-    snapshot_id           = string
-    throughput            = number
+    delete_on_termination = optional(bool, true)
+    device_name           = optional(string, "/dev/xvda")
+    encrypted             = optional(bool, true)
+    iops                  = optional(number)
+    kms_key_id            = optional(string)
+    snapshot_id           = optional(string)
+    throughput            = optional(number)
     volume_size           = number
-    volume_type           = string
+    volume_type           = optional(string, "gp3")
   }))
   default = [{
-    delete_on_termination = true
-    device_name           = "/dev/xvda"
-    encrypted             = true
-    iops                  = null
-    kms_key_id            = null
-    snapshot_id           = null
-    throughput            = null
-    volume_size           = 30
-    volume_type           = "gp3"
+    volume_size = 30
   }]
 }