diff --git a/builder/hyperv/common/step_clone_vm.go b/builder/hyperv/common/step_clone_vm.go
index 8233e8306..6ce856cf2 100644
--- a/builder/hyperv/common/step_clone_vm.go
+++ b/builder/hyperv/common/step_clone_vm.go
@@ -32,6 +32,7 @@ type StepCloneVM struct {
 	EnableVirtualizationExtensions bool
 	MacAddress                     string
 	KeepRegistered                 bool
+	AdditionalDiskSize             []uint
 }
 
 func (s *StepCloneVM) Run(ctx context.Context, state multistep.StateBag) multistep.StepAction {
@@ -125,6 +126,20 @@ func (s *StepCloneVM) Run(ctx context.Context, state multistep.StateBag) multist
 		}
 	}
 
+	if len(s.AdditionalDiskSize) > 0 {
+		for index, size := range s.AdditionalDiskSize {
+			diskSize := int64(size * 1024 * 1024)
+			diskFile := fmt.Sprintf("%s-%d.vhdx", s.VMName, index)
+			err = driver.AddVirtualMachineHardDrive(s.VMName, path, diskFile, diskSize, diskBlockSize, "SCSI")
+			if err != nil {
+				err := fmt.Errorf("Error creating and attaching additional disk drive: %s", err)
+				state.Put("error", err)
+				ui.Error(err.Error())
+				return multistep.ActionHalt
+			}
+		}
+	}
+
 	if s.MacAddress != "" {
 		err = driver.SetVmNetworkAdapterMacAddress(s.VMName, s.MacAddress)
 		if err != nil {
diff --git a/builder/hyperv/vmcx/builder.go b/builder/hyperv/vmcx/builder.go
index b95630706..d43a36500 100644
--- a/builder/hyperv/vmcx/builder.go
+++ b/builder/hyperv/vmcx/builder.go
@@ -59,6 +59,14 @@ type Config struct {
 	// Windows installs, which look for an Autounattend.xml file on removable
 	// media. By default, no secondary ISO will be attached.
 	SecondaryDvdImages []string `mapstructure:"secondary_iso_images" required:"false"`
+	// The size or sizes of any
+	// additional hard disks for the VM in megabytes. If this is not specified
+	// then the VM will only contain a primary hard disk. Additional drives
+	// will be attached to the SCSI interface only. The builder uses
+	// expandable rather than fixed-size virtual hard disks, so the actual
+	// file representing the disk will not use the full size unless it is
+	// full.
+	AdditionalDiskSize []uint `mapstructure:"disk_additional_size" required:"false"`
 	// If set to attach then attach and
 	// mount the ISO image specified in guest_additions_path. If set to
 	// none then guest additions are not attached and mounted; This is the
@@ -67,10 +75,8 @@ type Config struct {
 	// The path to the ISO image for guest
 	// additions.
 	GuestAdditionsPath string `mapstructure:"guest_additions_path" required:"false"`
-
 	// This is the path to a directory containing an exported virtual machine.
 	CloneFromVMCXPath string `mapstructure:"clone_from_vmcx_path"`
-
 	// This is the name of the virtual machine to clone from.
 	CloneFromVMName string `mapstructure:"clone_from_vm_name"`
 	// The name of a snapshot in the
@@ -354,7 +360,7 @@ func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
 		}
 	}
 
-	numberOfIsos := len(b.config.SecondaryDvdImages)
+	numberOfIsos := len(b.config.SecondaryDvdImages) + len(b.config.AdditionalDiskSize)
 
 	if b.config.GuestAdditionsMode == "attach" {
 		if _, err := os.Stat(b.config.GuestAdditionsPath); os.IsNotExist(err) {
@@ -524,6 +530,7 @@ func (b *Builder) Run(ctx context.Context, ui packer.Ui, hook packer.Hook) (pack
 			EnableVirtualizationExtensions: b.config.EnableVirtualizationExtensions,
 			MacAddress:                     b.config.MacAddress,
 			KeepRegistered:                 b.config.KeepRegistered,
+			AdditionalDiskSize:             b.config.AdditionalDiskSize,
 		},
 
 		&hypervcommon.StepEnableIntegrationService{},