diff --git a/internal/zenutil/env_darwin.go b/internal/zenutil/env_darwin.go
index 5b4a557..39b99f8 100644
--- a/internal/zenutil/env_darwin.go
+++ b/internal/zenutil/env_darwin.go
@@ -1,16 +1,7 @@
 package zenutil
 
-import "strconv"
-
 // These are internal.
 var (
 	Separator = "\x00"
 	LineBreak = "\n"
 )
-
-func ParseWindowId(id string) any {
-	if pid, err := strconv.ParseUint(id, 0, 64); err == nil {
-		return int(pid)
-	}
-	return id
-}
diff --git a/internal/zenutil/env_unix.go b/internal/zenutil/env_unix.go
index 79bbd6d..ad4003b 100644
--- a/internal/zenutil/env_unix.go
+++ b/internal/zenutil/env_unix.go
@@ -2,15 +2,8 @@
 
 package zenutil
 
-import "strconv"
-
 // These are internal.
 var (
 	Separator = "\x1e"
 	LineBreak = "\n"
 )
-
-func ParseWindowId(id string) int {
-	wid, _ := strconv.ParseUint(id, 0, 64)
-	return int(wid)
-}
diff --git a/internal/zenutil/env_windows.go b/internal/zenutil/env_windows.go
index 168e6c3..e8e1894 100644
--- a/internal/zenutil/env_windows.go
+++ b/internal/zenutil/env_windows.go
@@ -1,14 +1,7 @@
 package zenutil
 
-import "strconv"
-
 // These are internal.
 var (
 	Separator string
 	LineBreak = "\r\n"
 )
-
-func ParseWindowId(id string) uintptr {
-	hwnd, _ := strconv.ParseUint(id, 0, 64)
-	return uintptr(hwnd)
-}
diff --git a/internal/zenutil/window_darwin.go b/internal/zenutil/window_darwin.go
new file mode 100644
index 0000000..3bffc43
--- /dev/null
+++ b/internal/zenutil/window_darwin.go
@@ -0,0 +1,91 @@
+package zenutil
+
+import (
+	"os"
+	"strconv"
+	"syscall"
+	"unsafe"
+)
+
+// ParseWindowId is internal.
+func ParseWindowId(id string) any {
+	if pid, err := strconv.ParseUint(id, 0, 64); err == nil {
+		return int(pid)
+	}
+	return id
+}
+
+// GetParentWindowId is internal.
+func GetParentWindowId() int {
+	buf, err := sysctlKernProcAll()
+	if err != nil {
+		return 0
+	}
+
+	type kinfo_proc struct {
+		_    [40]byte
+		Pid  int32
+		_    [516]byte
+		PPid int32
+		_    [84]byte
+	}
+	const size = int(unsafe.Sizeof(kinfo_proc{}))
+
+	ppids := map[int]int{}
+	for i := 0; i+size < len(buf); i += size {
+		p := (*kinfo_proc)(unsafe.Pointer(&buf[i]))
+		ppids[int(p.Pid)] = int(p.PPid)
+	}
+
+	pid := os.Getppid()
+	for {
+		ppid := ppids[pid]
+		switch ppid {
+		case 0:
+			return 0
+		case 1:
+			return pid
+		default:
+			pid = ppid
+		}
+	}
+}
+
+func sysctlKernProcAll() ([]byte, error) {
+	const (
+		CTRL_KERN     = 1
+		KERN_PROC     = 14
+		KERN_PROC_ALL = 0
+	)
+
+	mib := [4]int32{CTRL_KERN, KERN_PROC, KERN_PROC_ALL, 0}
+	size := uintptr(0)
+
+	_, _, errno := syscall.Syscall6(
+		syscall.SYS___SYSCTL,
+		uintptr(unsafe.Pointer(&mib[0])),
+		uintptr(len(mib)),
+		0,
+		uintptr(unsafe.Pointer(&size)),
+		0,
+		0)
+
+	if errno != 0 {
+		return nil, errno
+	}
+
+	bs := make([]byte, size)
+	_, _, errno = syscall.Syscall6(
+		syscall.SYS___SYSCTL,
+		uintptr(unsafe.Pointer(&mib[0])),
+		uintptr(len(mib)),
+		uintptr(unsafe.Pointer(&bs[0])),
+		uintptr(unsafe.Pointer(&size)),
+		0,
+		0)
+
+	if errno != 0 {
+		return nil, errno
+	}
+	return bs[0:size], nil
+}
diff --git a/internal/zenutil/window_unix.go b/internal/zenutil/window_unix.go
new file mode 100644
index 0000000..d1598da
--- /dev/null
+++ b/internal/zenutil/window_unix.go
@@ -0,0 +1,42 @@
+//go:build !windows && !darwin
+
+package zenutil
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os/exec"
+	"strconv"
+)
+
+// ParseWindowId is internal.
+func ParseWindowId(id string) int {
+	wid, _ := strconv.ParseUint(id, 0, 64)
+	return int(wid)
+}
+
+// GetParentWindowId is internal.
+func GetParentWindowId() int {
+	buf, err := exec.Command("ps", "-xo", "pid=,ppid=").CombinedOutput()
+	if err != nil {
+		return 0
+	}
+
+	ppids := map[int]int{}
+	reader := bytes.NewReader(buf)
+	for {
+		var pid, ppid int
+		_, err := fmt.Fscan(reader, &pid, &ppid)
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return 0
+		}
+		ppids[pid] = ppid
+	}
+
+	// Find the relevant pid and window id.
+	return 0
+}
diff --git a/internal/zenutil/window_windows.go b/internal/zenutil/window_windows.go
new file mode 100644
index 0000000..f661732
--- /dev/null
+++ b/internal/zenutil/window_windows.go
@@ -0,0 +1,14 @@
+package zenutil
+
+import "strconv"
+
+// ParseWindowId is internal.
+func ParseWindowId(id string) uintptr {
+	hwnd, _ := strconv.ParseUint(id, 0, 64)
+	return uintptr(hwnd)
+}
+
+// GetParentWindowId is internal.
+func GetParentWindowId() int {
+	return 0
+}