diff --git a/src/kdefrontend/spreadsheet/DropValuesDialog.cpp b/src/kdefrontend/spreadsheet/DropValuesDialog.cpp
index 5c65b734c..39855fa2a 100644
--- a/src/kdefrontend/spreadsheet/DropValuesDialog.cpp
+++ b/src/kdefrontend/spreadsheet/DropValuesDialog.cpp
@@ -1,338 +1,345 @@
 /***************************************************************************
     File                 : DropValuesDialog.cpp
     Project              : LabPlot
     Description          : Dialog for droping and masking values in columns
     --------------------------------------------------------------------
     Copyright            : (C) 2015 by Alexander Semke (alexander.semke@web.de)
 
  ***************************************************************************/
 
 /***************************************************************************
  *                                                                         *
  *  This program 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 2 of the License, or      *
  *  (at your option) any later version.                                    *
  *                                                                         *
  *  This program 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 this program; if not, write to the Free Software           *
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor,                    *
  *   Boston, MA  02110-1301  USA                                           *
  *                                                                         *
  ***************************************************************************/
 #include "DropValuesDialog.h"
 #include "backend/core/column/Column.h"
 #include "backend/lib/macros.h"
 #include "backend/spreadsheet/Spreadsheet.h"
 
 #include <QThreadPool>
+#include <QDialogButtonBox>
+#include <QPushButton>
 #include <KLocalizedString>
 
 #include <cmath>
 
 /*!
 	\class DropValuesDialog
 	\brief Dialog for generating values from a mathematical function.
 
 	\ingroup kdefrontend
  */
 
-DropValuesDialog::DropValuesDialog(Spreadsheet* s, bool mask, QWidget* parent, Qt::WFlags fl) : KDialog(parent, fl),
+DropValuesDialog::DropValuesDialog(Spreadsheet* s, bool mask, QWidget* parent, Qt::WFlags fl) : QDialog(parent, fl),
 	m_spreadsheet(s), m_mask(mask) {
 
 	setWindowTitle(i18n("Drop values"));
 
-	QFrame* mainWidget = new QFrame(this);
-	ui.setupUi(mainWidget);
-	setMainWidget( mainWidget );
+	ui.setupUi(this);
     setAttribute(Qt::WA_DeleteOnClose);
 	ui.cbOperator->addItem(i18n("equal to"));
 	ui.cbOperator->addItem(i18n("between (including end points)"));
 	ui.cbOperator->addItem(i18n("between (excluding end points)"));
 	ui.cbOperator->addItem(i18n("greater then"));
 	ui.cbOperator->addItem(i18n("greater then or equal to"));
 	ui.cbOperator->addItem(i18n("lesser then"));
 	ui.cbOperator->addItem(i18n("lesser then or equal to"));
 
 	ui.leValue1->setValidator( new QDoubleValidator(ui.leValue1) );
 	ui.leValue2->setValidator( new QDoubleValidator(ui.leValue2) );
 
-	setButtons( KDialog::Ok | KDialog::Cancel );
+	QDialogButtonBox* btnBox = new QDialogButtonBox(QDialogButtonBox::Ok | QDialogButtonBox::Cancel);
+
+	ui.horizontalLayout->addWidget(btnBox);
+	m_okButton = btnBox->button(QDialogButtonBox::Ok);
+	QPushButton* cancelButton = btnBox->button(QDialogButtonBox::Cancel);
+
+	connect(cancelButton, SIGNAL(clicked(bool)), this, SLOT(close()));
+
 	if (m_mask) {
-		setButtonText(KDialog::Ok, i18n("&Mask"));
-		setButtonToolTip(KDialog::Ok, i18n("Mask values in the specified region"));
+		m_okButton->setText(i18n("&Mask"));
+		m_okButton->setToolTip(i18n("Mask values in the specified region"));
 		ui.lMode->setText(i18n("Mask values"));
 		setWindowTitle(i18n("Mask values"));
 	} else {
-		setButtonText(KDialog::Ok, i18n("&Drop"));
-		setButtonToolTip(KDialog::Ok, i18n("Drop values in the specified region"));
+		m_okButton->setText(i18n("&Drop"));
+		m_okButton->setToolTip(i18n("Drop values in the specified region"));
 	}
 
-	connect( ui.cbOperator, SIGNAL(currentIndexChanged(int)), this, SLOT(operatorChanged(int)) );
-	connect(this, SIGNAL(okClicked()), this, SLOT(okClicked()));
+	connect(ui.cbOperator, SIGNAL(currentIndexChanged(int)), this, SLOT(operatorChanged(int)) );
+	connect(m_okButton, SIGNAL(clicked(bool)), this, SLOT(okClicked()));
 
 	resize( QSize(400,0).expandedTo(minimumSize()) );
 	operatorChanged(0);
 }
 
 void DropValuesDialog::setColumns(QVector<Column*> columns) {
 	m_columns = columns;
 }
 
 void DropValuesDialog::operatorChanged(int index) const {
 	bool value2 = (index==1) || (index==2);
 	ui.lMin->setVisible(value2);
 	ui.lMax->setVisible(value2);
 	ui.lAnd->setVisible(value2);
 	ui.leValue2->setVisible(value2);
 }
 
 void DropValuesDialog::okClicked() const {
 	if (m_mask)
 		maskValues();
 	else
 		dropValues();
 }
 
 //TODO: m_column->setMasked() is slow, we need direct access to the masked-container -> redesign
 class MaskValuesTask : public QRunnable {
 	public:
 		MaskValuesTask(Column* col, int op, double value1, double value2){
 			m_column = col;
 			m_operator = op;
 			m_value1 = value1;
 			m_value2 = value2;
-		};
+		}
 
 		void run() {
 			m_column->setSuppressDataChangedSignal(true);
 			bool changed = false;
 			QVector<double>* data = static_cast<QVector<double>* >(m_column->data());
 
 			//equal to
 			if (m_operator == 0) {
 				for (int i=0; i<data->size(); ++i) {
 					if (data->at(i) == m_value1) {
 						m_column->setMasked(i, true);
 						changed = true;
 					}
 				}
 			}
 
 			//between (including end points)
 			else if (m_operator == 1) {
 				for (int i=0; i<data->size(); ++i) {
 					if (data->at(i) >= m_value1 && data->at(i) <= m_value2) {
 						m_column->setMasked(i, true);
 						changed = true;
 					}
 				}
 			}
 
 			//between (excluding end points)
 			else if (m_operator == 2) {
 				for (int i=0; i<data->size(); ++i) {
 					if (data->at(i) > m_value1 && data->at(i) < m_value2) {
 						m_column->setMasked(i, true);
 						changed = true;
 					}
 				}
 			}
 
-			//greater then
+			//greater than
 			else if (m_operator == 3) {
 				for (int i=0; i<data->size(); ++i) {
 					if (data->at(i) > m_value1) {
 						m_column->setMasked(i, true);
 						changed = true;
 					}
 				}
 			}
 
-			//greater then or equal to
+			//greater than or equal to
 			else if (m_operator == 4) {
 				for (int i=0; i<data->size(); ++i) {
 					if (data->at(i) >= m_value1) {
 						m_column->setMasked(i, true);
 						changed = true;
 					}
 				}
 			}
 
-			//lesser then
+			//lesser than
 			else if (m_operator == 5) {
 				for (int i=0; i<data->size(); ++i) {
 					if (data->at(i) < m_value1) {
 						m_column->setMasked(i, true);
 						changed = true;
 					}
 				}
 			}
 
-			//lesser then or equal to
+			//lesser than or equal to
 			else if (m_operator == 6) {
 				for (int i=0; i<data->size(); ++i) {
 					if (data->at(i) <= m_value1) {
 						m_column->setMasked(i, true);
 						changed = true;
 					}
 				}
 			}
 
 			m_column->setSuppressDataChangedSignal(false);
 			if (changed)
 				m_column->setChanged();
 		}
 
 	private:
 		Column* m_column;
 		int m_operator;
 		double m_value1;
 		double m_value2;
 };
 
 class DropValuesTask : public QRunnable {
 	public:
 		DropValuesTask(Column* col, int op, double value1, double value2){
 			m_column = col;
 			m_operator = op;
 			m_value1 = value1;
 			m_value2 = value2;
-		};
+		}
 
 		void run() {
 			bool changed = false;
 			QVector<double>* data = static_cast<QVector<double>* >(m_column->data());
 			QVector<double> new_data(*data);
 
 			//equal to
 			if (m_operator == 0) {
 				for (int i=0; i<new_data.size(); ++i) {
 					if (new_data[i] == m_value1) {
 						new_data[i] = NAN;
 						changed = true;
 					}
 				}
 			}
 
 			//between (including end points)
 			else if (m_operator == 1) {
 				for (int i=0; i<new_data.size(); ++i) {
 					if (new_data[i] >= m_value1 && new_data[i] <= m_value2) {
 						new_data[i] = NAN;
 						changed = true;
 					}
 				}
 			}
 
 			//between (excluding end points)
 			else if (m_operator == 2) {
 				for (int i=0; i<new_data.size(); ++i) {
 					if (new_data[i] > m_value1 && new_data[i] < m_value2) {
 						new_data[i] = NAN;
 						changed = true;
 					}
 				}
 			}
 
-			//greater then
+			//greater than
 			else if (m_operator == 3) {
 				for (int i=0; i<new_data.size(); ++i) {
 					if (new_data[i] > m_value1) {
 						new_data[i] = NAN;
 						changed = true;
 					}
 				}
 			}
 
-			//greater then or equal to
+			//greater than or equal to
 			else if (m_operator == 4) {
 				for (int i=0; i<new_data.size(); ++i) {
 					if (new_data[i] >= m_value1) {
 						new_data[i] = NAN;
 						changed = true;
 					}
 				}
 			}
 
-			//lesser then
+			//lesser than
 			else if (m_operator == 5) {
 				for (int i=0; i<new_data.size(); ++i) {
 					if (new_data[i] < m_value1) {
 						new_data[i] = NAN;
 						changed = true;
 					}
 				}
 			}
 
-			//lesser then or equal to
+			//lesser than or equal to
 			else if (m_operator == 6) {
 				for (int i=0; i<new_data.size(); ++i) {
 					if (new_data[i] <= m_value1) {
 						new_data[i] = NAN;
 						changed = true;
 					}
 				}
 			}
 
 			if (changed)
 				m_column->replaceValues(0, new_data);
 		}
 
 	private:
 		Column* m_column;
 		int m_operator;
 		double m_value1;
 		double m_value2;
 };
 
 void DropValuesDialog::maskValues() const {
 	Q_ASSERT(m_spreadsheet);
 
 	WAIT_CURSOR;
 	m_spreadsheet->beginMacro(i18n("%1: mask values", m_spreadsheet->name()));
 
 	const int op = ui.cbOperator->currentIndex();
 	const double value1 = ui.leValue1->text().toDouble();
 	const double value2 = ui.leValue2->text().toDouble();
 
 	foreach(Column* col, m_columns) {
 		MaskValuesTask* task = new MaskValuesTask(col, op, value1, value2);
 		task->run();
 		//TODO: writing to the undo-stack in Column::setMasked() is not tread-safe -> redesign
 // 		QThreadPool::globalInstance()->start(task);
 	}
 
 	//wait until all columns were processed
 // 	QThreadPool::globalInstance()->waitForDone();
 
 	m_spreadsheet->endMacro();
 	RESET_CURSOR;
 }
 
 void DropValuesDialog::dropValues() const {
 	Q_ASSERT(m_spreadsheet);
 
 	WAIT_CURSOR;
 	m_spreadsheet->beginMacro(i18n("%1: drop values", m_spreadsheet->name()));
 
 	const int op = ui.cbOperator->currentIndex();
 	const double value1 = ui.leValue1->text().toDouble();
 	const double value2 = ui.leValue2->text().toDouble();
 
 	foreach(Column* col, m_columns) {
 		DropValuesTask* task = new DropValuesTask(col, op, value1, value2);
 		QThreadPool::globalInstance()->start(task);
 	}
 
 	//wait until all columns were processed
 	QThreadPool::globalInstance()->waitForDone();
 
 	m_spreadsheet->endMacro();
 	RESET_CURSOR;
 }
diff --git a/src/kdefrontend/spreadsheet/DropValuesDialog.h b/src/kdefrontend/spreadsheet/DropValuesDialog.h
index 67129447a..5ce039276 100644
--- a/src/kdefrontend/spreadsheet/DropValuesDialog.h
+++ b/src/kdefrontend/spreadsheet/DropValuesDialog.h
@@ -1,59 +1,60 @@
 /***************************************************************************
     File                 : DropValuesDialog.h
     Project              : LabPlot
     Description          : Dialog for droping and masking values in columns
     --------------------------------------------------------------------
     Copyright            : (C) 2015 by Alexander Semke (alexander.semke@web.de)
 
  ***************************************************************************/
 
 /***************************************************************************
  *                                                                         *
  *  This program 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 2 of the License, or      *
  *  (at your option) any later version.                                    *
  *                                                                         *
  *  This program 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 this program; if not, write to the Free Software           *
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor,                    *
  *   Boston, MA  02110-1301  USA                                           *
  *                                                                         *
  ***************************************************************************/
 #ifndef DROPVALUESDIALOG_H
 #define DROPVALUESDIALOG_H
 
 #include "ui_dropvalueswidget.h"
-#include <KDialog>
+#include <QDialog>
 
 
 class Column;
 class Spreadsheet;
-
-class DropValuesDialog : public KDialog {
+class QPushButton;
+class DropValuesDialog : public QDialog {
 	Q_OBJECT
 
 	public:
 		explicit DropValuesDialog(Spreadsheet* s, bool mask = false, QWidget* parent = 0, Qt::WFlags fl = 0);
 		void setColumns(QVector<Column*>);
 
 	private:
 		Ui::DropValuesWidget ui;
 		QVector<Column*> m_columns;
 		Spreadsheet* m_spreadsheet;
 		bool m_mask;
 
 		void dropValues() const;
 		void maskValues() const;
 
+		QPushButton* m_okButton;
 	private slots:
 		void operatorChanged(int) const;
 		void okClicked() const;
 };
 
 #endif