diff --git a/iso/builder_acc_test.go b/iso/builder_acc_test.go
index d1c94c67c..14cc6a6cc 100644
--- a/iso/builder_acc_test.go
+++ b/iso/builder_acc_test.go
@@ -31,7 +31,9 @@ func defaultConfig() map[string]interface{} {
 		"ssh_username": "root",
 		"ssh_password": "jetbrains",
 
-		"vm_name":      commonT.NewVMName(),
+		"vm_name":   commonT.NewVMName(),
+		"disk_size": 2,
+
 		"communicator": "none", // do not start the VM without any bootable devices
 	}
 
diff --git a/iso/config.go b/iso/config.go
index 6646d3235..2b29c67ba 100644
--- a/iso/config.go
+++ b/iso/config.go
@@ -6,6 +6,7 @@ import (
 	"github.com/hashicorp/packer/packer"
 	"github.com/hashicorp/packer/template/interpolate"
 	"github.com/jetbrains-infra/packer-builder-vsphere/common"
+	"fmt"
 )
 
 type Config struct {
@@ -35,6 +36,9 @@ func NewConfig(raws ...interface{}) (*Config, []string, error) {
 	errs = packer.MultiErrorAppend(errs, c.RunConfig.Prepare()...)
 	errs = packer.MultiErrorAppend(errs, c.ConnectConfig.Prepare()...)
 	errs = packer.MultiErrorAppend(errs, c.HardwareConfig.Prepare()...)
+	if c.DiskSize <= 0 {
+		errs = packer.MultiErrorAppend(errs, fmt.Errorf("'disk_size' must be provided"))
+	}
 	errs = packer.MultiErrorAppend(errs, c.ShutdownConfig.Prepare()...)
 	errs = packer.MultiErrorAppend(errs, c.CreateConfig.Prepare()...)