diff --git a/cmd/zenity/main.go b/cmd/zenity/main.go
index d61d36b..60473ad 100644
--- a/cmd/zenity/main.go
+++ b/cmd/zenity/main.go
@@ -452,10 +452,13 @@ func loadFlags() []zenity.Option {
 	if attach != "" {
 		opts = append(opts, zenity.Attach(zenutil.ParseWindowId(attach)))
 	} else if modal {
-		if pid := zenutil.GetParentWindowId(); pid != 0 {
-			opts = append(opts, zenity.Attach(pid))
+		if id := zenutil.GetParentWindowId(os.Getppid()); id != 0 {
+			opts = append(opts, zenity.Attach(id))
 		}
 	}
+	if modal {
+		opts = append(opts, zenity.Modal())
+	}
 
 	// Message options
 
diff --git a/internal/zenutil/window_darwin.go b/internal/zenutil/window_darwin.go
index 51c74df..acdbcee 100644
--- a/internal/zenutil/window_darwin.go
+++ b/internal/zenutil/window_darwin.go
@@ -1,7 +1,6 @@
 package zenutil
 
 import (
-	"os"
 	"strconv"
 
 	"golang.org/x/sys/unix"
@@ -16,8 +15,7 @@ func ParseWindowId(id string) any {
 }
 
 // GetParentWindowId is internal.
-func GetParentWindowId() int {
-	pid := os.Getppid()
+func GetParentWindowId(pid int) int {
 	for {
 		kinfo, err := unix.SysctlKinfoProc("kern.proc.pid", pid)
 		if err != nil {
diff --git a/internal/zenutil/window_unix.go b/internal/zenutil/window_unix.go
index d1598da..a95cd3c 100644
--- a/internal/zenutil/window_unix.go
+++ b/internal/zenutil/window_unix.go
@@ -8,6 +8,7 @@ import (
 	"io"
 	"os/exec"
 	"strconv"
+	"strings"
 )
 
 // ParseWindowId is internal.
@@ -17,14 +18,38 @@ func ParseWindowId(id string) int {
 }
 
 // GetParentWindowId is internal.
-func GetParentWindowId() int {
-	buf, err := exec.Command("ps", "-xo", "pid=,ppid=").CombinedOutput()
+func GetParentWindowId(pid int) int {
+	winids, err := getPidToWindowMap()
 	if err != nil {
 		return 0
 	}
 
+	ppids, err := getPidToPpidMap()
+	if err != nil {
+		return 0
+	}
+
+	for {
+		if winid, ok := winids[pid]; ok {
+			id, _ := strconv.Atoi(winid)
+			return id
+		}
+		if ppid, ok := ppids[pid]; ok {
+			pid = ppid
+		} else {
+			return 0
+		}
+	}
+}
+
+func getPidToPpidMap() (map[int]int, error) {
+	out, err := exec.Command("ps", "-xo", "pid=,ppid=").Output()
+	if err != nil {
+		return nil, err
+	}
+
 	ppids := map[int]int{}
-	reader := bytes.NewReader(buf)
+	reader := bytes.NewReader(out)
 	for {
 		var pid, ppid int
 		_, err := fmt.Fscan(reader, &pid, &ppid)
@@ -32,11 +57,58 @@ func GetParentWindowId() int {
 			break
 		}
 		if err != nil {
-			return 0
+			return nil, err
 		}
 		ppids[pid] = ppid
 	}
-
-	// Find the relevant pid and window id.
-	return 0
+	return ppids, nil
+}
+
+func getPidToWindowMap() (map[int]string, error) {
+	ids, err := getWindowIDs()
+	if err != nil {
+		return nil, err
+	}
+
+	var pid int
+	winids := map[int]string{}
+	for _, id := range ids {
+		pid, err = getWindowPid(id)
+		if err != nil {
+			continue
+		}
+		winids[pid] = id
+	}
+	if err != nil && len(winids) == 0 {
+		return nil, err
+	}
+	return winids, nil
+}
+
+func getWindowIDs() ([]string, error) {
+	out, err := exec.Command("xprop", "-root", "0i", "\t$0+", "_NET_CLIENT_LIST").Output()
+	if err != nil {
+		return nil, err
+	}
+
+	if i := bytes.IndexByte(out, '\t'); i < 0 {
+		return nil, fmt.Errorf("xprop: unexpected output: %q", out)
+	} else {
+		out = out[i+1:]
+	}
+	return strings.Split(string(out), ", "), nil
+}
+
+func getWindowPid(id string) (int, error) {
+	out, err := exec.Command("xprop", "-id", id, "0i", "\t$0", "_NET_WM_PID").Output()
+	if err != nil {
+		return 0, err
+	}
+
+	if i := bytes.IndexByte(out, '\t'); i < 0 {
+		return 0, fmt.Errorf("xprop: unexpected output: %q", out)
+	} else {
+		out = out[i+1:]
+	}
+	return strconv.Atoi(string(out))
 }
diff --git a/internal/zenutil/window_windows.go b/internal/zenutil/window_windows.go
index f661732..14eef03 100644
--- a/internal/zenutil/window_windows.go
+++ b/internal/zenutil/window_windows.go
@@ -9,6 +9,6 @@ func ParseWindowId(id string) uintptr {
 }
 
 // GetParentWindowId is internal.
-func GetParentWindowId() int {
+func GetParentWindowId(pid int) int {
 	return 0
 }