diff --git a/src/ltui/textarea.lua b/src/ltui/textarea.lua
index 54de807..98e1ddd 100644
--- a/src/ltui/textarea.lua
+++ b/src/ltui/textarea.lua
@@ -67,9 +67,14 @@ function textarea:text_set(text)
     return label.text_set(self, text)
 end
 
+-- is scrollable?
+function textarea:scrollable()
+    return self._LINECOUNT > self:height()
+end
+
 -- scroll
 function textarea:scroll(lines)
-    if self._LINECOUNT > self:height() then
+    if self:scrollable() then
         self._STARTLINE = self._STARTLINE + lines
         if self._STARTLINE < 0 then
             self._STARTLINE = 0
@@ -85,7 +90,7 @@ end
 
 -- scroll to end
 function textarea:scroll_to_end()
-    if self._LINECOUNT > self:height() then
+    if self:scrollable() then
         local startline_end = self._LINECOUNT - self:height()
         self._STARTLINE = startline_end
         self:action_on(action.ac_on_scrolled, self._STARTLINE / startline_end)
diff --git a/src/ltui/textdialog.lua b/src/ltui/textdialog.lua
index d88599f..cfec53c 100644
--- a/src/ltui/textdialog.lua
+++ b/src/ltui/textdialog.lua
@@ -59,9 +59,22 @@ function textdialog:init(name, bounds, title)
         end
     end)
 
+    -- show scrollbar?
+    self:text():action_set(action.ac_on_text_changed, function (v)
+        if self:option("scrollable") then
+            if v:scrollable() then
+                self:scrollbar():show(true)
+            else
+                self:scrollbar():show(false)
+            end
+        end
+    end)
+
     -- on scroll for text and scrollbar
     self:text():action_set(action.ac_on_scrolled, function (v, progress)
-        self:scrollbar():progress_set(progress)
+        if self:option("scrollable") then
+            self:scrollbar():progress_set(progress)
+        end
     end)
 end
 
@@ -72,12 +85,9 @@ function textdialog:option_set(name, value)
         if value ~= oldvalue then
             if value then
                 self:text():bounds():resize(self:panel():width() - 1, self:panel():height() - 1)
-                self:scrollbar():show(true)
             else
                 self:text():bounds():resize(self:panel():width(), self:panel():height() - 1)
-                self:scrollbar():show(false)
             end
-            self:invalidate()
         end
     end
     dialog.option_set(self, name, value)
diff --git a/tests/dialog.lua b/tests/dialog.lua
index 1e8371d..68dec0f 100644
--- a/tests/dialog.lua
+++ b/tests/dialog.lua
@@ -76,6 +76,7 @@ function demo:dialog_help()
     local dialog_help = self._DIALOG_HELP
     if not dialog_help then
         dialog_help = textdialog:new("dialog.help", rect {1, 1, self:width() - 1, self:height() - 1}, "README")
+        dialog_help:option_set("scrollable", true)
         local helptext = nil
         local file = io.open("./LICENSE.md", 'r')
         if file then
@@ -86,7 +87,6 @@ function demo:dialog_help()
             dialog_help:text():text_set(helptext)
         end
         dialog_help:button_add("exit", "< Exit >", function (v) self:remove(dialog_help) end)
-        dialog_help:option_set("scrollable", true)
         self._DIALOG_HELP = dialog_help
     end
     return dialog_help