diff --git a/azurerm/resource_arm_kubernetes_cluster.go b/azurerm/resource_arm_kubernetes_cluster.go
index 7ed601042132..9979d6746678 100644
--- a/azurerm/resource_arm_kubernetes_cluster.go
+++ b/azurerm/resource_arm_kubernetes_cluster.go
@@ -204,9 +204,11 @@ func resourceArmKubernetesCluster() *schema.Resource {
 						},
 
 						"os_disk_size_gb": {
-							Type:     schema.TypeInt,
-							Optional: true,
-							ForceNew: true,
+							Type:         schema.TypeInt,
+							Optional:     true,
+							ForceNew:     true,
+							Computed:     true,
+							ValidateFunc: validation.IntAtLeast(1),
 						},
 
 						"vnet_subnet_id": {