diff --git a/helper/deprecated.go b/helper/deprecated.go
new file mode 100644
index 0000000..f09b0c8
--- /dev/null
+++ b/helper/deprecated.go
@@ -0,0 +1,73 @@
+// Package helper exposes the internal/helper package.
+//
+// Deprecated: This package will be removed in 0.4.
+package helper
+
+import (
+	"context"
+	"io"
+	"os"
+	"os/exec"
+	"time"
+	_ "unsafe" // for go:linkname
+
+	"hakurei.app/container"
+	"hakurei.app/container/check"
+	"hakurei.app/internal/helper"
+	"hakurei.app/message"
+)
+
+//go:linkname WaitDelay hakurei.app/internal/helper.WaitDelay
+var WaitDelay time.Duration
+
+const (
+	// HakureiHelper is set to 1 when args fd is enabled and 0 otherwise.
+	HakureiHelper = helper.HakureiHelper
+	// HakureiStatus is set to 1 when stat fd is enabled and 0 otherwise.
+	HakureiStatus = helper.HakureiStatus
+)
+
+type Helper = helper.Helper
+
+// NewCheckedArgs returns a checked null-terminated argument writer for a copy of args.
+//
+//go:linkname NewCheckedArgs hakurei.app/internal/helper.NewCheckedArgs
+func NewCheckedArgs(args ...string) (wt io.WriterTo, err error)
+
+// MustNewCheckedArgs returns a checked null-terminated argument writer for a copy of args.
+// If s contains a NUL byte this function panics instead of returning an error.
+//
+//go:linkname MustNewCheckedArgs hakurei.app/internal/helper.MustNewCheckedArgs
+func MustNewCheckedArgs(args ...string) io.WriterTo
+
+// NewDirect initialises a new direct Helper instance with wt as the null-terminated argument writer.
+// Function argF returns an array of arguments passed directly to the child process.
+//
+//go:linkname NewDirect hakurei.app/internal/helper.NewDirect
+func NewDirect(
+	ctx context.Context,
+	name string,
+	wt io.WriterTo,
+	stat bool,
+	argF func(argsFd, statFd int) []string,
+	cmdF func(cmd *exec.Cmd),
+	extraFiles []*os.File,
+) Helper
+
+// New initialises a Helper instance with wt as the null-terminated argument writer.
+//
+//go:linkname New hakurei.app/internal/helper.New
+func New(
+	ctx context.Context,
+	msg message.Msg,
+	pathname *check.Absolute, name string,
+	wt io.WriterTo,
+	stat bool,
+	argF func(argsFd, statFd int) []string,
+	cmdF func(z *container.Container),
+	extraFiles []*os.File,
+) Helper
+
+// InternalHelperStub is an internal function but exported because it is cross-package;
+// it is part of the implementation of the helper stub.
+func InternalHelperStub() { helper.InternalHelperStub() }
diff --git a/helper/proc/deprecated.go b/helper/proc/deprecated.go
new file mode 100644
index 0000000..9189752
--- /dev/null
+++ b/helper/proc/deprecated.go
@@ -0,0 +1,63 @@
+// Deprecated: This package will be removed in 0.4.
+package proc
+
+import (
+	"context"
+	"io"
+	"os"
+	"os/exec"
+	"time"
+	_ "unsafe" // for go:linkname
+
+	"hakurei.app/internal/helper/proc"
+)
+
+//go:linkname FulfillmentTimeout hakurei.app/internal/helper/proc.FulfillmentTimeout
+var FulfillmentTimeout time.Duration
+
+// A File is an extra file with deferred initialisation.
+type File = proc.File
+
+// ExtraFilesPre is a linked list storing addresses of [os.File].
+type ExtraFilesPre = proc.ExtraFilesPre
+
+// Fulfill calls the [File.Fulfill] method on all files, starts cmd and blocks until all fulfillment completes.
+//
+//go:linkname Fulfill hakurei.app/internal/helper/proc.Fulfill
+func Fulfill(ctx context.Context,
+	v *[]*os.File, start func() error,
+	files []File, extraFiles *ExtraFilesPre,
+) (err error)
+
+// InitFile initialises f as part of the slice extraFiles points to,
+// and returns its final fd value.
+//
+//go:linkname InitFile hakurei.app/internal/helper/proc.InitFile
+func InitFile(f File, extraFiles *ExtraFilesPre) (fd uintptr)
+
+// BaseFile implements the Init method of the File interface and provides indirect access to extra file state.
+type BaseFile = proc.BaseFile
+
+//go:linkname ExtraFile hakurei.app/internal/helper/proc.ExtraFile
+func ExtraFile(cmd *exec.Cmd, f *os.File) (fd uintptr)
+
+//go:linkname ExtraFileSlice hakurei.app/internal/helper/proc.ExtraFileSlice
+func ExtraFileSlice(extraFiles *[]*os.File, f *os.File) (fd uintptr)
+
+// NewWriterTo returns a [File] that receives content from wt on fulfillment.
+//
+//go:linkname NewWriterTo hakurei.app/internal/helper/proc.NewWriterTo
+func NewWriterTo(wt io.WriterTo) File
+
+// NewStat returns a [File] implementing the behaviour
+// of the receiving end of xdg-dbus-proxy stat fd.
+//
+//go:linkname NewStat hakurei.app/internal/helper/proc.NewStat
+func NewStat(s *io.Closer) File
+
+var (
+	//go:linkname ErrStatFault hakurei.app/internal/helper/proc.ErrStatFault
+	ErrStatFault error
+	//go:linkname ErrStatRead hakurei.app/internal/helper/proc.ErrStatRead
+	ErrStatRead error
+)
diff --git a/helper/args.go b/internal/helper/args.go
similarity index 100%
rename from helper/args.go
rename to internal/helper/args.go
diff --git a/helper/args_test.go b/internal/helper/args_test.go
similarity index 96%
rename from helper/args_test.go
rename to internal/helper/args_test.go
index d6225c3..c83c679 100644
--- a/helper/args_test.go
+++ b/internal/helper/args_test.go
@@ -7,7 +7,7 @@ import (
 	"syscall"
 	"testing"
 
-	"hakurei.app/helper"
+	"hakurei.app/internal/helper"
 )
 
 func TestArgsString(t *testing.T) {
diff --git a/helper/cmd.go b/internal/helper/cmd.go
similarity index 98%
rename from helper/cmd.go
rename to internal/helper/cmd.go
index 9a5bc3a..babceb2 100644
--- a/helper/cmd.go
+++ b/internal/helper/cmd.go
@@ -10,7 +10,7 @@ import (
 	"sync"
 	"syscall"
 
-	"hakurei.app/helper/proc"
+	"hakurei.app/internal/helper/proc"
 )
 
 // NewDirect initialises a new direct Helper instance with wt as the null-terminated argument writer.
diff --git a/helper/cmd_test.go b/internal/helper/cmd_test.go
similarity index 96%
rename from helper/cmd_test.go
rename to internal/helper/cmd_test.go
index 64ac643..3d29479 100644
--- a/helper/cmd_test.go
+++ b/internal/helper/cmd_test.go
@@ -9,7 +9,7 @@ import (
 	"testing"
 
 	"hakurei.app/container"
-	"hakurei.app/helper"
+	"hakurei.app/internal/helper"
 )
 
 func TestCmd(t *testing.T) {
diff --git a/helper/container.go b/internal/helper/container.go
similarity index 97%
rename from helper/container.go
rename to internal/helper/container.go
index b85f585..56a5195 100644
--- a/helper/container.go
+++ b/internal/helper/container.go
@@ -11,7 +11,7 @@ import (
 
 	"hakurei.app/container"
 	"hakurei.app/container/check"
-	"hakurei.app/helper/proc"
+	"hakurei.app/internal/helper/proc"
 	"hakurei.app/message"
 )
 
diff --git a/helper/container_test.go b/internal/helper/container_test.go
similarity index 97%
rename from helper/container_test.go
rename to internal/helper/container_test.go
index 922d825..f55da75 100644
--- a/helper/container_test.go
+++ b/internal/helper/container_test.go
@@ -9,7 +9,7 @@ import (
 	"hakurei.app/container"
 	"hakurei.app/container/check"
 	"hakurei.app/container/fhs"
-	"hakurei.app/helper"
+	"hakurei.app/internal/helper"
 )
 
 func TestContainer(t *testing.T) {
diff --git a/helper/helper.go b/internal/helper/helper.go
similarity index 97%
rename from helper/helper.go
rename to internal/helper/helper.go
index 60bd761..378d947 100644
--- a/helper/helper.go
+++ b/internal/helper/helper.go
@@ -8,7 +8,7 @@ import (
 	"os"
 	"time"
 
-	"hakurei.app/helper/proc"
+	"hakurei.app/internal/helper/proc"
 )
 
 var WaitDelay = 2 * time.Second
diff --git a/helper/helper_test.go b/internal/helper/helper_test.go
similarity index 99%
rename from helper/helper_test.go
rename to internal/helper/helper_test.go
index 4cc36d3..dae098b 100644
--- a/helper/helper_test.go
+++ b/internal/helper/helper_test.go
@@ -13,7 +13,7 @@ import (
 	"testing"
 	"time"
 
-	"hakurei.app/helper"
+	"hakurei.app/internal/helper"
 )
 
 var (
diff --git a/helper/proc/files.go b/internal/helper/proc/files.go
similarity index 100%
rename from helper/proc/files.go
rename to internal/helper/proc/files.go
diff --git a/helper/proc/pipe.go b/internal/helper/proc/pipe.go
similarity index 100%
rename from helper/proc/pipe.go
rename to internal/helper/proc/pipe.go
diff --git a/helper/stub.go b/internal/helper/stub.go
similarity index 100%
rename from helper/stub.go
rename to internal/helper/stub.go
diff --git a/helper/stub_test.go b/internal/helper/stub_test.go
similarity index 85%
rename from helper/stub_test.go
rename to internal/helper/stub_test.go
index 58a2538..4b438a5 100644
--- a/helper/stub_test.go
+++ b/internal/helper/stub_test.go
@@ -5,7 +5,7 @@ import (
 	"testing"
 
 	"hakurei.app/container"
-	"hakurei.app/helper"
+	"hakurei.app/internal/helper"
 )
 
 func TestMain(m *testing.M) { container.TryArgv0(nil); helper.InternalHelperStub(); os.Exit(m.Run()) }