diff --git a/plugins/python/mixer_slider_docker/ui_mixer_slider_docker.py b/plugins/python/mixer_slider_docker/ui_mixer_slider_docker.py
index 025d7a332f..92d0674a1c 100644
--- a/plugins/python/mixer_slider_docker/ui_mixer_slider_docker.py
+++ b/plugins/python/mixer_slider_docker/ui_mixer_slider_docker.py
@@ -1,56 +1,56 @@
 '''
     Copyright (C) 2019 Tusooa Zhu <tusooa@vista.aero>
 
     This file is part of Krita-docker-color-slider.
 
     Krita-docker-color-slider is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation, either version 3 of the License, or
     (at your option) any later version.
 
     Krita-docker-color-slider is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.
 
     You should have received a copy of the GNU General Public License
     along with Krita-docker-color-slider.  If not, see <https://www.gnu.org/licenses/>.
 '''
-from PyQt5.QtWidgets import QDialogButtonBox, QLabel, QVBoxLayout, QHBoxLayout, QLineEdit
+from PyQt5.QtWidgets import QDialogButtonBox, QLabel, QVBoxLayout, QHBoxLayout, QSpinBox
 from PyQt5.QtGui import QIntValidator
 from PyQt5.QtCore import Qt
 import krita
 
 from .settings_dialog import SettingsDialog
 
 
 class UIMixerSliderDocker(object):
     def __init__(self):
         self.krita_instance = krita.Krita.instance()
         self.main_dialog = SettingsDialog(self, self.krita_instance.activeWindow().qwindow())
 
         self.button_box = QDialogButtonBox(self.main_dialog)
         self.vbox = QVBoxLayout(self.main_dialog)
         self.hbox = QHBoxLayout(self.main_dialog)
         self.line_edit = None
 
         self.button_box.accepted.connect(self.main_dialog.accept)
         self.button_box.rejected.connect(self.main_dialog.reject)
 
         self.button_box.setOrientation(Qt.Horizontal)
         self.button_box.setStandardButtons(QDialogButtonBox.Ok | QDialogButtonBox.Cancel)
 
     def initialize(self, docker):
         self.docker = docker
 
         self.vbox.addLayout(self.hbox)
         self.hbox.addWidget(QLabel(i18n('Number of slider lines: ')))
-        self.line_edit = QLineEdit(str(len(docker.sliders)))
-        self.line_edit.setValidator(QIntValidator(1, 8))
+        self.line_edit = QSpinBox()
+        self.line_edit.setValue(len(docker.sliders))
         self.hbox.addWidget(self.line_edit)
 
         self.vbox.addWidget(self.button_box)
 
         self.main_dialog.show()
         self.main_dialog.activateWindow()
         self.main_dialog.exec_()