diff --git a/specification/compute/resource-manager/Microsoft.Compute/stable/2017-12-01/compute.json b/specification/compute/resource-manager/Microsoft.Compute/stable/2017-12-01/compute.json
index ad3343bbeb54..5f3cfca6a12f 100644
--- a/specification/compute/resource-manager/Microsoft.Compute/stable/2017-12-01/compute.json
+++ b/specification/compute/resource-manager/Microsoft.Compute/stable/2017-12-01/compute.json
@@ -3083,6 +3083,66 @@
       }
     },
     "/subscriptions/{subscriptionId}/resourceGroups/{resourceGroupName}/providers/Microsoft.Compute/virtualMachineScaleSets/{vmScaleSetName}/virtualmachines/{instanceId}": {
+      "put": {
+        "tags": [
+          "VirtualMachineScaleSetVMs"
+        ],
+        "operationId": "VirtualMachineScaleSetVMs_Update",
+        "description": "Updates a virtual machine of a VM scale set.",
+        "parameters": [
+          {
+            "name": "resourceGroupName",
+            "in": "path",
+            "required": true,
+            "type": "string",
+            "description": "The name of the resource group."
+          },
+          {
+            "name": "vmScaleSetName",
+            "in": "path",
+            "required": true,
+            "type": "string",
+            "description": "The name of the VM scale set where the extension should be create or updated."
+          },
+          {
+            "name": "instanceId",
+            "in": "path",
+            "required": true,
+            "type": "string",
+            "description": "The instance ID of the virtual machine."
+          },
+          {
+            "name": "parameters",
+            "in": "body",
+            "required": true,
+            "schema": {
+              "$ref": "#/definitions/VirtualMachineScaleSetVM"
+            },
+            "description": "Parameters supplied to the Update Virtual Machine Scale Sets VM operation."
+          },
+          {
+            "$ref": "#/parameters/ApiVersionParameter"
+          },
+          {
+            "$ref": "#/parameters/SubscriptionIdParameter"
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "OK",
+            "schema": {
+              "$ref": "#/definitions/VirtualMachineScaleSetVM"
+            }
+          },
+          "202": {
+            "description": "Accepted",
+            "schema": {
+              "$ref": "#/definitions/VirtualMachineScaleSetVM"
+            }
+          }
+        },
+        "x-ms-long-running-operation": true
+      },
       "delete": {
         "tags": [
           "VirtualMachineScaleSetVMs"