diff --git a/cmd/zenity/main.go b/cmd/zenity/main.go
index 60473ad..31aae19 100644
--- a/cmd/zenity/main.go
+++ b/cmd/zenity/main.go
@@ -450,9 +450,9 @@ func loadFlags() []zenity.Option {
 	}
 
 	if attach != "" {
-		opts = append(opts, zenity.Attach(zenutil.ParseWindowId(attach)))
+		opts = append(opts, zenity.Attach(zencmd.ParseWindowId(attach)))
 	} else if modal {
-		if id := zenutil.GetParentWindowId(os.Getppid()); id != 0 {
+		if id := zencmd.GetParentWindowId(os.Getppid()); id != 0 {
 			opts = append(opts, zenity.Attach(id))
 		}
 	}
diff --git a/cmd/zenity/progress.go b/cmd/zenity/progress.go
index d545b56..a2f2d59 100644
--- a/cmd/zenity/progress.go
+++ b/cmd/zenity/progress.go
@@ -10,6 +10,7 @@ import (
 	"strings"
 
 	"github.com/ncruces/zenity"
+	"github.com/ncruces/zenity/internal/zencmd"
 )
 
 func progress(opts ...zenity.Option) (err error) {
@@ -21,7 +22,7 @@ func progress(opts ...zenity.Option) (err error) {
 	if autoKill {
 		defer func() {
 			if err == zenity.ErrCanceled {
-				killParent()
+				zencmd.KillParent()
 			}
 		}()
 	}
diff --git a/cmd/zenity/progress_windows.go b/cmd/zenity/progress_windows.go
deleted file mode 100644
index 6563f08..0000000
--- a/cmd/zenity/progress_windows.go
+++ /dev/null
@@ -1,3 +0,0 @@
-package main
-
-func killParent() {}
diff --git a/cmd/zenity/progress_unix.go b/internal/zencmd/process_unix.go
similarity index 62%
rename from cmd/zenity/progress_unix.go
rename to internal/zencmd/process_unix.go
index b6769ba..adb43d3 100644
--- a/cmd/zenity/progress_unix.go
+++ b/internal/zencmd/process_unix.go
@@ -1,12 +1,13 @@
 //go:build darwin || dev
 
-package main
+package zencmd
 
 import (
 	"os"
 	"syscall"
 )
 
-func killParent() {
+// KillParent is internal.
+func KillParent() {
 	syscall.Kill(os.Getppid(), syscall.SIGHUP)
 }
diff --git a/internal/zencmd/process_windows.go b/internal/zencmd/process_windows.go
new file mode 100644
index 0000000..f279430
--- /dev/null
+++ b/internal/zencmd/process_windows.go
@@ -0,0 +1,4 @@
+package zencmd
+
+// KillParent is internal.
+func KillParent() {}
diff --git a/internal/zenutil/window_darwin.go b/internal/zencmd/window_darwin.go
similarity index 92%
rename from internal/zenutil/window_darwin.go
rename to internal/zencmd/window_darwin.go
index acdbcee..70ab603 100644
--- a/internal/zenutil/window_darwin.go
+++ b/internal/zencmd/window_darwin.go
@@ -1,4 +1,4 @@
-package zenutil
+package zencmd
 
 import (
 	"strconv"
@@ -6,6 +6,8 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+type any = interface{}
+
 // ParseWindowId is internal.
 func ParseWindowId(id string) any {
 	if pid, err := strconv.ParseUint(id, 0, 64); err == nil {
diff --git a/internal/zenutil/window_unix.go b/internal/zencmd/window_unix.go
similarity index 99%
rename from internal/zenutil/window_unix.go
rename to internal/zencmd/window_unix.go
index a95cd3c..c20fe3b 100644
--- a/internal/zenutil/window_unix.go
+++ b/internal/zencmd/window_unix.go
@@ -1,6 +1,6 @@
 //go:build !windows && !darwin
 
-package zenutil
+package zencmd
 
 import (
 	"bytes"
diff --git a/internal/zenutil/window_windows.go b/internal/zencmd/window_windows.go
similarity index 94%
rename from internal/zenutil/window_windows.go
rename to internal/zencmd/window_windows.go
index b92d98d..24ff5fe 100644
--- a/internal/zenutil/window_windows.go
+++ b/internal/zencmd/window_windows.go
@@ -1,4 +1,4 @@
-package zenutil
+package zencmd
 
 import (
 	"strconv"
diff --git a/zenity_test.go b/zenity_test.go
index 5b57d47..9ca6c85 100644
--- a/zenity_test.go
+++ b/zenity_test.go
@@ -7,7 +7,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/ncruces/zenity/internal/zenutil"
+	"github.com/ncruces/zenity/internal/zencmd"
 )
 
 func Test_applyOptions(t *testing.T) {
@@ -30,7 +30,7 @@ func Test_applyOptions(t *testing.T) {
 		{name: "Icon", args: Icon(ErrorIcon), want: options{icon: ErrorIcon}},
 		{name: "Icon", args: Icon("error"), want: options{icon: "error"}},
 		{name: "Modal", args: Modal(), want: options{modal: true}},
-		{name: "Attach", args: Attach(zenutil.ParseWindowId("12345")), want: options{attach: zenutil.ParseWindowId("12345")}},
+		{name: "Attach", args: Attach(zencmd.ParseWindowId("12345")), want: options{attach: zencmd.ParseWindowId("12345")}},
 
 		// Message options
 		{name: "NoWrap", args: NoWrap(), want: options{noWrap: true}},