diff --git a/internal/win/gdi32.go b/internal/win/gdi32.go
index 9dfb75b..933f6f1 100644
--- a/internal/win/gdi32.go
+++ b/internal/win/gdi32.go
@@ -27,4 +27,4 @@ type LOGFONT struct {
 
 //sys CreateFontIndirect(lf *LOGFONT) (font Handle) = gdi32.CreateFontIndirectW
 //sys DeleteObject(o Handle) (ok bool) = gdi32.DeleteObject
-//sys GetDeviceCaps(dc Handle, index int) (cap uintptr) = gdi32.GetDeviceCaps
+//sys GetDeviceCaps(dc Handle, index int) (cap int) = gdi32.GetDeviceCaps
diff --git a/internal/win/generate.go b/internal/win/generate.go
index cd3060a..5a681c8 100644
--- a/internal/win/generate.go
+++ b/internal/win/generate.go
@@ -1,6 +1,6 @@
 //go:build generate
 
 //go:generate -command mkwinsyscall go run golang.org/x/sys/windows/mkwinsyscall -output zsyscall_windows.go
-//go:generate mkwinsyscall comctl32.go comdlg32.go gdi32.go ole32.go shell32.go user32.go
+//go:generate mkwinsyscall comctl32.go comdlg32.go gdi32.go ole32.go shell32.go user32.go win32.go wtsapi32.go
 
 package win
diff --git a/internal/win/ole32.go b/internal/win/ole32.go
index ea617eb..7be6ded 100644
--- a/internal/win/ole32.go
+++ b/internal/win/ole32.go
@@ -44,4 +44,4 @@ func (o *COMObject) Call(trap uintptr, a ...uintptr) (r1, r2 uintptr, lastErr er
 }
 
 //sys CoTaskMemFree(address uintptr) = ole32.CoTaskMemFree
-//sys CoCreateInstance(clsid uintptr, unkOuter unsafe.Pointer, clsContext int32, iid uintptr, address unsafe.Pointer) (ret error) = ole32.CoCreateInstance
+//sys CoCreateInstance(clsid uintptr, unkOuter unsafe.Pointer, clsContext int32, iid uintptr, address unsafe.Pointer) (res error) = ole32.CoCreateInstance
diff --git a/internal/win/shell32.go b/internal/win/shell32.go
index 97bd834..fb00314 100644
--- a/internal/win/shell32.go
+++ b/internal/win/shell32.go
@@ -53,6 +53,6 @@ type _IShellItemVtbl struct {
 }
 
 //sys SHBrowseForFolder(bi *BROWSEINFO) (ptr uintptr) = shell32.SHBrowseForFolder
-//sys SHCreateItemFromParsingName(path *uint16, bc unsafe.Pointer, iid uintptr, item **IShellItem) (err error) = shell32.SHCreateItemFromParsingName
-//sys SHGetPathFromIDListEx(ptr uintptr, path *uint16, pathLen int, opts int) (err error) = shell32.SHGetPathFromIDListEx
+//sys SHCreateItemFromParsingName(path *uint16, bc unsafe.Pointer, iid uintptr, item **IShellItem) (res error) = shell32.SHCreateItemFromParsingName
+//sys SHGetPathFromIDListEx(ptr uintptr, path *uint16, pathLen int, opts int) (ok bool) = shell32.SHGetPathFromIDListEx
 //sys ShellNotifyIcon(message uint32, data *NOTIFYICONDATA) (ret int, err error) = shell32.Shell_NotifyIconW
diff --git a/internal/win/user32.go b/internal/win/user32.go
index 26c94ca..6d1e16b 100644
--- a/internal/win/user32.go
+++ b/internal/win/user32.go
@@ -32,3 +32,5 @@ const (
 func MessageBox(hwnd HWND, text *uint16, caption *uint16, boxtype uint32) (ret int32, err error) {
 	return windows.MessageBox(hwnd, text, caption, boxtype)
 }
+
+//sys GetDlgCtrlID(wnd HWND) (ret int) = user32.GetDlgCtrlID
diff --git a/internal/win/win32.go b/internal/win/win32.go
index ebf0d87..d989756 100644
--- a/internal/win/win32.go
+++ b/internal/win/win32.go
@@ -7,3 +7,5 @@ import "golang.org/x/sys/windows"
 
 type Handle = windows.Handle
 type HWND = windows.HWND
+
+//sys RtlGetNtVersionNumbers(major *uint32, minor *uint32, build *uint32) = ntdll.RtlGetNtVersionNumbers
diff --git a/internal/win/wtsapi32.go b/internal/win/wtsapi32.go
new file mode 100644
index 0000000..5df6f8c
--- /dev/null
+++ b/internal/win/wtsapi32.go
@@ -0,0 +1,10 @@
+//go:build windows
+
+package win
+
+const (
+	WTS_CURRENT_SERVER_HANDLE = 0
+	WTS_CURRENT_SESSION       = 0xffffffff
+)
+
+//sys WTSSendMessage(server Handle, sessionID uint32, title *uint16, titleLength int, message *uint16, messageLength int, style uint32, timeout int, response *uint32, wait bool) (err error) = wtsapi32.WTSSendMessageW
diff --git a/internal/win/zsyscall_windows.go b/internal/win/zsyscall_windows.go
index 66b5cf5..10a1c85 100644
--- a/internal/win/zsyscall_windows.go
+++ b/internal/win/zsyscall_windows.go
@@ -41,8 +41,11 @@ var (
 	modcomctl32 = windows.NewLazySystemDLL("comctl32.dll")
 	modcomdlg32 = windows.NewLazySystemDLL("comdlg32.dll")
 	modgdi32    = windows.NewLazySystemDLL("gdi32.dll")
+	modntdll    = windows.NewLazySystemDLL("ntdll.dll")
 	modole32    = windows.NewLazySystemDLL("ole32.dll")
 	modshell32  = windows.NewLazySystemDLL("shell32.dll")
+	moduser32   = windows.NewLazySystemDLL("user32.dll")
+	modwtsapi32 = windows.NewLazySystemDLL("wtsapi32.dll")
 
 	procInitCommonControlsEx        = modcomctl32.NewProc("InitCommonControlsEx")
 	procChooseColorW                = modcomdlg32.NewProc("ChooseColorW")
@@ -52,12 +55,15 @@ var (
 	procCreateFontIndirectW         = modgdi32.NewProc("CreateFontIndirectW")
 	procDeleteObject                = modgdi32.NewProc("DeleteObject")
 	procGetDeviceCaps               = modgdi32.NewProc("GetDeviceCaps")
+	procRtlGetNtVersionNumbers      = modntdll.NewProc("RtlGetNtVersionNumbers")
 	procCoCreateInstance            = modole32.NewProc("CoCreateInstance")
 	procCoTaskMemFree               = modole32.NewProc("CoTaskMemFree")
 	procSHBrowseForFolder           = modshell32.NewProc("SHBrowseForFolder")
 	procSHCreateItemFromParsingName = modshell32.NewProc("SHCreateItemFromParsingName")
 	procSHGetPathFromIDListEx       = modshell32.NewProc("SHGetPathFromIDListEx")
 	procShell_NotifyIconW           = modshell32.NewProc("Shell_NotifyIconW")
+	procGetDlgCtrlID                = moduser32.NewProc("GetDlgCtrlID")
+	procWTSSendMessageW             = modwtsapi32.NewProc("WTSSendMessageW")
 )
 
 func InitCommonControlsEx(icc *INITCOMMONCONTROLSEX) (ok bool) {
@@ -102,16 +108,21 @@ func DeleteObject(o Handle) (ok bool) {
 	return
 }
 
-func GetDeviceCaps(dc Handle, index int) (cap uintptr) {
+func GetDeviceCaps(dc Handle, index int) (cap int) {
 	r0, _, _ := syscall.Syscall(procGetDeviceCaps.Addr(), 2, uintptr(dc), uintptr(index), 0)
-	cap = uintptr(r0)
+	cap = int(r0)
 	return
 }
 
-func CoCreateInstance(clsid uintptr, unkOuter unsafe.Pointer, clsContext int32, iid uintptr, address unsafe.Pointer) (ret error) {
+func RtlGetNtVersionNumbers(major *uint32, minor *uint32, build *uint32) {
+	syscall.Syscall(procRtlGetNtVersionNumbers.Addr(), 3, uintptr(unsafe.Pointer(major)), uintptr(unsafe.Pointer(minor)), uintptr(unsafe.Pointer(build)))
+	return
+}
+
+func CoCreateInstance(clsid uintptr, unkOuter unsafe.Pointer, clsContext int32, iid uintptr, address unsafe.Pointer) (res error) {
 	r0, _, _ := syscall.Syscall6(procCoCreateInstance.Addr(), 5, uintptr(clsid), uintptr(unkOuter), uintptr(clsContext), uintptr(iid), uintptr(address), 0)
 	if r0 != 0 {
-		ret = syscall.Errno(r0)
+		res = syscall.Errno(r0)
 	}
 	return
 }
@@ -127,19 +138,17 @@ func SHBrowseForFolder(bi *BROWSEINFO) (ptr uintptr) {
 	return
 }
 
-func SHCreateItemFromParsingName(path *uint16, bc unsafe.Pointer, iid uintptr, item **IShellItem) (err error) {
-	r1, _, e1 := syscall.Syscall6(procSHCreateItemFromParsingName.Addr(), 4, uintptr(unsafe.Pointer(path)), uintptr(bc), uintptr(iid), uintptr(unsafe.Pointer(item)), 0, 0)
-	if r1 == 0 {
-		err = errnoErr(e1)
+func SHCreateItemFromParsingName(path *uint16, bc unsafe.Pointer, iid uintptr, item **IShellItem) (res error) {
+	r0, _, _ := syscall.Syscall6(procSHCreateItemFromParsingName.Addr(), 4, uintptr(unsafe.Pointer(path)), uintptr(bc), uintptr(iid), uintptr(unsafe.Pointer(item)), 0, 0)
+	if r0 != 0 {
+		res = syscall.Errno(r0)
 	}
 	return
 }
 
-func SHGetPathFromIDListEx(ptr uintptr, path *uint16, pathLen int, opts int) (err error) {
-	r1, _, e1 := syscall.Syscall6(procSHGetPathFromIDListEx.Addr(), 4, uintptr(ptr), uintptr(unsafe.Pointer(path)), uintptr(pathLen), uintptr(opts), 0, 0)
-	if r1 == 0 {
-		err = errnoErr(e1)
-	}
+func SHGetPathFromIDListEx(ptr uintptr, path *uint16, pathLen int, opts int) (ok bool) {
+	r0, _, _ := syscall.Syscall6(procSHGetPathFromIDListEx.Addr(), 4, uintptr(ptr), uintptr(unsafe.Pointer(path)), uintptr(pathLen), uintptr(opts), 0, 0)
+	ok = r0 != 0
 	return
 }
 
@@ -151,3 +160,21 @@ func ShellNotifyIcon(message uint32, data *NOTIFYICONDATA) (ret int, err error)
 	}
 	return
 }
+
+func GetDlgCtrlID(wnd HWND) (ret int) {
+	r0, _, _ := syscall.Syscall(procGetDlgCtrlID.Addr(), 1, uintptr(wnd), 0, 0)
+	ret = int(r0)
+	return
+}
+
+func WTSSendMessage(server Handle, sessionID uint32, title *uint16, titleLength int, message *uint16, messageLength int, style uint32, timeout int, response *uint32, wait bool) (err error) {
+	var _p0 uint32
+	if wait {
+		_p0 = 1
+	}
+	r1, _, e1 := syscall.Syscall12(procWTSSendMessageW.Addr(), 10, uintptr(server), uintptr(sessionID), uintptr(unsafe.Pointer(title)), uintptr(titleLength), uintptr(unsafe.Pointer(message)), uintptr(messageLength), uintptr(style), uintptr(timeout), uintptr(unsafe.Pointer(response)), uintptr(_p0), 0, 0)
+	if r1 == 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
diff --git a/msg_windows.go b/msg_windows.go
index 9ec5fec..8923ca9 100644
--- a/msg_windows.go
+++ b/msg_windows.go
@@ -8,10 +8,6 @@ import (
 	"github.com/ncruces/zenity/internal/win"
 )
 
-var (
-	getDlgCtrlID = user32.NewProc("GetDlgCtrlID")
-)
-
 func message(kind messageKind, text string, opts options) error {
 	var flags uint32
 
@@ -22,6 +18,8 @@ func message(kind messageKind, text string, opts options) error {
 		flags |= win.MB_OKCANCEL
 	case opts.extraButton != nil:
 		flags |= win.MB_YESNO
+	default:
+		opts.cancelLabel = opts.okLabel
 	}
 
 	switch opts.icon {
@@ -59,7 +57,7 @@ func message(kind messageKind, text string, opts options) error {
 	defer setup()()
 
 	if opts.ctx != nil || opts.okLabel != nil || opts.cancelLabel != nil || opts.extraButton != nil || opts.icon != nil {
-		unhook, err := hookMessageDialog(kind, opts)
+		unhook, err := hookMessageDialog(opts)
 		if err != nil {
 			return err
 		}
@@ -89,7 +87,7 @@ func message(kind messageKind, text string, opts options) error {
 	}
 }
 
-func hookMessageDialog(kind messageKind, opts options) (unhook context.CancelFunc, err error) {
+func hookMessageDialog(opts options) (unhook context.CancelFunc, err error) {
 	return hookDialog(opts.ctx, opts.windowIcon, nil, func(wnd uintptr) {
 		enumChildWindows.Call(wnd,
 			syscall.NewCallback(hookMessageDialogCallback),
@@ -97,8 +95,8 @@ func hookMessageDialog(kind messageKind, opts options) (unhook context.CancelFun
 	})
 }
 
-func hookMessageDialogCallback(wnd uintptr, lparam *options) uintptr {
-	ctl, _, _ := getDlgCtrlID.Call(wnd)
+func hookMessageDialogCallback(wnd win.HWND, lparam *options) uintptr {
+	ctl := win.GetDlgCtrlID(wnd)
 
 	var text *string
 	switch ctl {
@@ -110,14 +108,14 @@ func hookMessageDialogCallback(wnd uintptr, lparam *options) uintptr {
 		text = lparam.extraButton
 	}
 	if text != nil {
-		setWindowText.Call(wnd, strptr(*text))
+		setWindowText.Call(uintptr(wnd), strptr(*text))
 	}
 
 	if ctl == 20 /*IDC_STATIC_OK*/ {
 		icon := getIcon(lparam.icon)
 		if icon.handle != 0 {
 			defer icon.delete()
-			sendMessage.Call(wnd, _STM_SETICON, icon.handle, 0)
+			sendMessage.Call(uintptr(wnd), _STM_SETICON, icon.handle, 0)
 		}
 	}
 	return 1
diff --git a/notify_windows.go b/notify_windows.go
index 9143cc4..12df65f 100644
--- a/notify_windows.go
+++ b/notify_windows.go
@@ -11,11 +11,6 @@ import (
 	"github.com/ncruces/zenity/internal/zenutil"
 )
 
-var (
-	rtlGetNtVersionNumbers = ntdll.NewProc("RtlGetNtVersionNumbers")
-	wtsSendMessage         = wtsapi32.NewProc("WTSSendMessageW")
-)
-
 func notify(text string, opts options) error {
 	if opts.ctx != nil && opts.ctx.Err() != nil {
 		return opts.ctx.Err()
@@ -64,10 +59,7 @@ func notify(text string, opts options) error {
 	}
 
 	var major, minor, build uint32
-	rtlGetNtVersionNumbers.Call(
-		uintptr(unsafe.Pointer(&major)),
-		uintptr(unsafe.Pointer(&minor)),
-		uintptr(unsafe.Pointer(&build)))
+	win.RtlGetNtVersionNumbers(&major, &minor, &build)
 
 	// On Windows 7 (6.1) and lower, wait up to 10 seconds to clean up.
 	if major < 6 || major == 6 && minor < 2 {
@@ -86,7 +78,7 @@ func notify(text string, opts options) error {
 }
 
 func wtsMessage(text string, opts options) error {
-	var flags uintptr
+	var flags uint32
 
 	switch opts.icon {
 	case ErrorIcon:
@@ -113,15 +105,8 @@ func wtsMessage(text string, opts options) error {
 	ptitle := syscall.StringToUTF16(*title)
 
 	var res uint32
-	s, _, err := wtsSendMessage.Call(
-		0,          // WTS_CURRENT_SERVER_HANDLE
-		0xffffffff, // WTS_CURRENT_SESSION
-		uintptr(unsafe.Pointer(&ptitle[0])), uintptr(2*len(ptitle)),
-		uintptr(unsafe.Pointer(&ptext[0])), uintptr(2*len(ptext)),
-		flags, uintptr(timeout), uintptr(unsafe.Pointer(&res)), 0)
-
-	if s == 0 {
-		return err
-	}
-	return nil
+	return win.WTSSendMessage(
+		win.WTS_CURRENT_SERVER_HANDLE, win.WTS_CURRENT_SESSION,
+		&ptitle[0], 2*len(ptitle), &ptext[0], 2*len(ptext),
+		flags, timeout, &res, false)
 }
diff --git a/util_windows.go b/util_windows.go
index 549a5fd..335f662 100644
--- a/util_windows.go
+++ b/util_windows.go
@@ -18,9 +18,7 @@ import (
 
 var (
 	kernel32 = windows.NewLazySystemDLL("kernel32.dll")
-	ntdll    = windows.NewLazySystemDLL("ntdll.dll")
 	user32   = windows.NewLazySystemDLL("user32.dll")
-	wtsapi32 = windows.NewLazySystemDLL("wtsapi32.dll")
 
 	activateActCtx     = kernel32.NewProc("ActivateActCtx")
 	createActCtx       = kernel32.NewProc("CreateActCtxW")
@@ -261,7 +259,7 @@ func getDPI(wnd uintptr) dpi {
 	if wnd != 0 && getDpiForWindow.Find() == nil {
 		res, _, _ = getDpiForWindow.Call(wnd)
 	} else if dc, _, _ := getWindowDC.Call(wnd); dc != 0 {
-		res = win.GetDeviceCaps(win.Handle(dc), win.LOGPIXELSY)
+		res = uintptr(win.GetDeviceCaps(win.Handle(dc), win.LOGPIXELSY))
 		releaseDC.Call(0, dc)
 	}