diff --git a/src/modules/partition/CMakeLists.txt b/src/modules/partition/CMakeLists.txt
index 753e8eae6..0b99a9dff 100644
--- a/src/modules/partition/CMakeLists.txt
+++ b/src/modules/partition/CMakeLists.txt
@@ -40,6 +40,7 @@ calamares_add_plugin( partition
         PartitionModel.cpp
         PartitionPage.cpp
         PartitionPreview.cpp
+        PartitionSizeController.cpp
         PartitionSizeWidget.cpp
         PartitionViewStep.cpp
         PMUtils.cpp
diff --git a/src/modules/partition/EditExistingPartitionDialog.cpp b/src/modules/partition/EditExistingPartitionDialog.cpp
index e946fec91..6a991143f 100644
--- a/src/modules/partition/EditExistingPartitionDialog.cpp
+++ b/src/modules/partition/EditExistingPartitionDialog.cpp
@@ -20,6 +20,7 @@
 
 #include <PartitionCoreModule.h>
 #include <PartitionInfo.h>
+#include <PartitionSizeController.h>
 #include <PMUtils.h>
 #include <ui_EditExistingPartitionDialog.h>
 #include <utils/Logger.h>
@@ -27,6 +28,7 @@
 // CalaPM
 #include <core/device.h>
 #include <core/partition.h>
+#include <fs/filesystemfactory.h>
 
 // Qt
 #include <QComboBox>
@@ -36,10 +38,37 @@ EditExistingPartitionDialog::EditExistingPartitionDialog( Device* device, Partit
     , m_ui( new Ui_EditExistingPartitionDialog )
     , m_device( device )
     , m_partition( partition )
+    , m_partitionSizeController( new PartitionSizeController( this ) )
 {
     m_ui->setupUi( this );
-    m_ui->sizeSpinBox->init( device, partition );
+
+    // Create a partition for partResizerWidget because it alters the first and
+    // last sectors when used
+    FileSystem* fs = FileSystemFactory::create(
+                         m_partition->fileSystem().type(),
+                         m_partition->firstSector(),
+                         m_partition->lastSector()
+                     );
+    m_partResizerWidgetPartition.reset( new Partition(
+                                            m_partition->parent(),
+                                            *m_device,
+                                            m_partition->roles(),
+                                            fs, fs->firstSector(), fs->lastSector(),
+                                            m_partition->partitionPath()
+                                        )
+                                      );
+
+    m_partitionSizeController->init( m_device, m_partResizerWidgetPartition.data() );
+    m_partitionSizeController->setSpinBox( m_ui->sizeSpinBox );
+
     m_ui->mountPointComboBox->setCurrentText( PartitionInfo::mountPoint( partition ) );
+
+    replacePartResizerWidget();
+
+    connect( m_ui->formatRadioButton, &QAbstractButton::toggled, [ this ]( bool )
+    {
+        replacePartResizerWidget();
+    } );
 }
 
 EditExistingPartitionDialog::~EditExistingPartitionDialog()
@@ -50,9 +79,12 @@ EditExistingPartitionDialog::applyChanges( PartitionCoreModule* core )
 {
     PartitionInfo::setMountPoint( m_partition, m_ui->mountPointComboBox->currentText() );
 
-    if ( m_ui->sizeSpinBox->isDirty() )
+    qint64 newFirstSector = m_partResizerWidgetPartition->firstSector();
+    qint64 newLastSector = m_partResizerWidgetPartition->lastSector();
+    bool partitionChanged = newFirstSector != m_partition->firstSector() || newLastSector != m_partition->lastSector();
+
+    if ( partitionChanged )
     {
-        PartitionSizeWidget::SectorRange range = m_ui->sizeSpinBox->sectorRange();
         if ( m_ui->formatRadioButton->isChecked() )
         {
             Partition* newPartition = PMUtils::createNewPartition(
@@ -60,8 +92,8 @@ EditExistingPartitionDialog::applyChanges( PartitionCoreModule* core )
                                           *m_device,
                                           m_partition->roles(),
                                           m_partition->fileSystem().type(),
-                                          range.first,
-                                          range.second );
+                                          newFirstSector,
+                                          newLastSector );
             PartitionInfo::setMountPoint( newPartition, PartitionInfo::mountPoint( m_partition ) );
             PartitionInfo::setFormat( newPartition, true );
 
@@ -69,7 +101,7 @@ EditExistingPartitionDialog::applyChanges( PartitionCoreModule* core )
             core->createPartition( m_device, newPartition );
         }
         else
-            core->resizePartition( m_device, m_partition, range.first, range.second );
+            core->resizePartition( m_device, m_partition, newFirstSector, newLastSector );
     }
     else
     {
@@ -80,3 +112,39 @@ EditExistingPartitionDialog::applyChanges( PartitionCoreModule* core )
             core->refreshPartition( m_device, m_partition );
     }
 }
+
+void
+EditExistingPartitionDialog::replacePartResizerWidget()
+{
+    /*
+     * There is no way to reliably update the partition used by
+     * PartResizerWidget, which is necessary when we switch between "format" and
+     * "keep". This is a hack which replaces the existing PartResizerWidget
+     * with a new one.
+     */
+
+    bool format = m_ui->formatRadioButton->isChecked();
+
+    qint64 used = format ? 0 : m_partition->fileSystem().sectorsUsed();
+    m_partResizerWidgetPartition->fileSystem().setSectorsUsed( used );
+
+    qint64 minFirstSector = m_partition->firstSector() - m_device->partitionTable()->freeSectorsBefore( *m_partition );
+    qint64 maxLastSector = m_partition->lastSector() + m_device->partitionTable()->freeSectorsAfter( *m_partition );
+
+    PartResizerWidget* widget = new PartResizerWidget( this );
+    widget->init( *m_device, *m_partResizerWidgetPartition, minFirstSector, maxLastSector );
+
+    if ( !format )
+    {
+        // If we are not formatting, make sure the space between the first and
+        // last sectors is big enough to fit the existing content.
+        widget->updateLastSector( m_partResizerWidgetPartition->lastSector() );
+        widget->updateFirstSector( m_partResizerWidgetPartition->firstSector() );
+    }
+
+    layout()->replaceWidget( m_ui->partResizerWidget, widget );
+    delete m_ui->partResizerWidget;
+    m_ui->partResizerWidget = widget;
+
+    m_partitionSizeController->setPartResizerWidget( widget );
+}
diff --git a/src/modules/partition/EditExistingPartitionDialog.h b/src/modules/partition/EditExistingPartitionDialog.h
index 270bbb0e5..779e318d0 100644
--- a/src/modules/partition/EditExistingPartitionDialog.h
+++ b/src/modules/partition/EditExistingPartitionDialog.h
@@ -25,6 +25,7 @@
 class PartitionCoreModule;
 class Device;
 class Partition;
+class PartitionSizeController;
 class Ui_EditExistingPartitionDialog;
 
 class EditExistingPartitionDialog : public QDialog
@@ -40,6 +41,10 @@ private:
     QScopedPointer< Ui_EditExistingPartitionDialog > m_ui;
     Device* m_device;
     Partition* m_partition;
+    QScopedPointer< Partition > m_partResizerWidgetPartition;
+    PartitionSizeController* m_partitionSizeController;
+
+    void replacePartResizerWidget();
 };
 
 #endif /* EDITEXISTINGPARTITIONDIALOG_H */
diff --git a/src/modules/partition/EditExistingPartitionDialog.ui b/src/modules/partition/EditExistingPartitionDialog.ui
index 3cbfeebd7..3618302b3 100644
--- a/src/modules/partition/EditExistingPartitionDialog.ui
+++ b/src/modules/partition/EditExistingPartitionDialog.ui
@@ -7,11 +7,11 @@
     <x>0</x>
     <y>0</y>
     <width>350</width>
-    <height>203</height>
+    <height>236</height>
    </rect>
   </property>
   <property name="sizePolicy">
-   <sizepolicy hsizetype="Minimum" vsizetype="Minimum">
+   <sizepolicy hsizetype="Preferred" vsizetype="Minimum">
     <horstretch>0</horstretch>
     <verstretch>0</verstretch>
    </sizepolicy>
@@ -20,29 +20,31 @@
    <string>Edit Existing Partition</string>
   </property>
   <layout class="QVBoxLayout" name="verticalLayout">
+   <property name="sizeConstraint">
+    <enum>QLayout::SetMinimumSize</enum>
+   </property>
+   <item>
+    <widget class="PartResizerWidget" name="partResizerWidget" native="true">
+     <property name="sizePolicy">
+      <sizepolicy hsizetype="Expanding" vsizetype="Fixed">
+       <horstretch>0</horstretch>
+       <verstretch>0</verstretch>
+      </sizepolicy>
+     </property>
+     <property name="minimumSize">
+      <size>
+       <width>0</width>
+       <height>59</height>
+      </size>
+     </property>
+    </widget>
+   </item>
    <item>
     <layout class="QFormLayout" name="formLayout">
      <property name="fieldGrowthPolicy">
       <enum>QFormLayout::ExpandingFieldsGrow</enum>
      </property>
-     <item row="0" column="0">
-      <widget class="QLabel" name="label">
-       <property name="text">
-        <string>Si&amp;ze:</string>
-       </property>
-       <property name="buddy">
-        <cstring>sizeSpinBox</cstring>
-       </property>
-      </widget>
-     </item>
-     <item row="0" column="1">
-      <widget class="PartitionSizeWidget" name="sizeSpinBox">
-       <property name="suffix">
-        <string> MB</string>
-       </property>
-      </widget>
-     </item>
-     <item row="1" column="0">
+     <item row="2" column="0">
       <widget class="QLabel" name="label_3">
        <property name="text">
         <string>Content:</string>
@@ -52,7 +54,7 @@
        </property>
       </widget>
      </item>
-     <item row="1" column="1">
+     <item row="2" column="1">
       <widget class="QRadioButton" name="keepRadioButton">
        <property name="text">
         <string>Keep</string>
@@ -62,15 +64,21 @@
        </property>
       </widget>
      </item>
-     <item row="2" column="1">
+     <item row="3" column="1">
       <widget class="QRadioButton" name="formatRadioButton">
        <property name="text">
         <string>Format</string>
        </property>
       </widget>
      </item>
-     <item row="3" column="1">
+     <item row="4" column="1">
       <widget class="QLabel" name="label_2">
+       <property name="sizePolicy">
+        <sizepolicy hsizetype="Expanding" vsizetype="Fixed">
+         <horstretch>0</horstretch>
+         <verstretch>0</verstretch>
+        </sizepolicy>
+       </property>
        <property name="text">
         <string>Warning: Formatting the partition will erase all existing data.</string>
        </property>
@@ -129,6 +137,19 @@
        </item>
       </widget>
      </item>
+     <item row="1" column="0">
+      <widget class="QLabel" name="label">
+       <property name="text">
+        <string>Size:</string>
+       </property>
+       <property name="buddy">
+        <cstring>sizeSpinBox</cstring>
+       </property>
+      </widget>
+     </item>
+     <item row="1" column="1">
+      <widget class="QSpinBox" name="sizeSpinBox"/>
+     </item>
     </layout>
    </item>
    <item>
@@ -145,9 +166,10 @@
  </widget>
  <customwidgets>
   <customwidget>
-   <class>PartitionSizeWidget</class>
-   <extends>QSpinBox</extends>
-   <header location="global">PartitionSizeWidget.h</header>
+   <class>PartResizerWidget</class>
+   <extends>QWidget</extends>
+   <header location="global">gui/partresizerwidget.h</header>
+   <container>1</container>
   </customwidget>
  </customwidgets>
  <tabstops>
diff --git a/src/modules/partition/PartitionSizeController.cpp b/src/modules/partition/PartitionSizeController.cpp
new file mode 100644
index 000000000..25f25151f
--- /dev/null
+++ b/src/modules/partition/PartitionSizeController.cpp
@@ -0,0 +1,115 @@
+/* === This file is part of Calamares - <http://github.com/calamares> ===
+ *
+ *   Copyright 2014, Aurélien Gâteau <agateau@kde.org>
+ *
+ *   Calamares 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.
+ *
+ *   Calamares 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 Calamares. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <PartitionSizeController.h>
+
+// Qt
+#include <QSpinBox>
+
+// CalaPM
+#include <core/device.h>
+#include <core/partition.h>
+#include <gui/partresizerwidget.h>
+
+// stdc++
+#include <limits>
+
+PartitionSizeController::PartitionSizeController( QObject* parent )
+    : QObject( parent )
+{}
+
+void
+PartitionSizeController::setPartResizerWidget( PartResizerWidget* widget )
+{
+    if ( m_partResizerWidget )
+        disconnect( m_partResizerWidget, 0, this, 0 );
+    m_partResizerWidget = widget;
+    // FIXME: Should be set by PartResizerWidget itself
+    m_partResizerWidget->setFixedHeight( PartResizerWidget::handleHeight() );
+    updateConnections();
+}
+
+void
+PartitionSizeController::setSpinBox( QSpinBox* spinBox )
+{
+    if ( m_spinBox )
+        disconnect( m_spinBox, 0, this, 0 );
+    m_spinBox = spinBox;
+    m_spinBox->setMaximum( std::numeric_limits< int >::max() );
+    updateConnections();
+}
+
+void
+PartitionSizeController::init( Device* device, Partition* partition )
+{
+    m_device = device;
+    m_partition = partition;
+}
+
+void
+PartitionSizeController::updateConnections()
+{
+    if ( !m_spinBox || !m_partResizerWidget )
+        return;
+
+    connect( m_spinBox, SIGNAL( editingFinished() ), SLOT( updatePartResizerWidget() ) );
+    connect( m_partResizerWidget, SIGNAL( firstSectorChanged( qint64 ) ), SLOT( updateSpinBox() ) );
+    connect( m_partResizerWidget, SIGNAL( lastSectorChanged( qint64 ) ), SLOT( updateSpinBox() ) );
+    updateSpinBox();
+}
+
+void
+PartitionSizeController::updatePartResizerWidget()
+{
+    if ( m_updating )
+        return;
+    m_updating = true;
+    qint64 sectorSize = qint64( m_spinBox->value() ) * 1024 * 1024 / m_device->logicalSectorSize();
+
+    qint64 firstSector = m_partition->firstSector();
+    qint64 lastSector = firstSector + sectorSize - 1;
+    if ( lastSector > m_partResizerWidget->maximumLastSector() )
+    {
+        qint64 delta = lastSector - m_partResizerWidget->maximumLastSector();
+        firstSector -= delta;
+        lastSector -= delta;
+    }
+    m_partResizerWidget->updateLastSector( lastSector );
+    m_partResizerWidget->updateFirstSector( firstSector );
+
+    // Update spinbox value in case it was an impossible value
+    doUpdateSpinBox();
+    m_updating = false;
+}
+
+void
+PartitionSizeController::updateSpinBox()
+{
+    if ( m_updating )
+        return;
+    m_updating = true;
+    doUpdateSpinBox();
+    m_updating = false;
+}
+
+void
+PartitionSizeController::doUpdateSpinBox()
+{
+    qint64 mbSize = ( m_partition->lastSector() - m_partition->firstSector() + 1 ) * m_device->logicalSectorSize() / 1024 / 1024;
+    m_spinBox->setValue( mbSize );
+}
diff --git a/src/modules/partition/PartitionSizeController.h b/src/modules/partition/PartitionSizeController.h
new file mode 100644
index 000000000..6b1e0e204
--- /dev/null
+++ b/src/modules/partition/PartitionSizeController.h
@@ -0,0 +1,57 @@
+/* === This file is part of Calamares - <http://github.com/calamares> ===
+ *
+ *   Copyright 2014, Aurélien Gâteau <agateau@kde.org>
+ *
+ *   Calamares 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.
+ *
+ *   Calamares 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 Calamares. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef PARTITIONSIZECONTROLLER_H
+#define PARTITIONSIZECONTROLLER_H
+
+#include <QObject>
+
+class QSpinBox;
+
+class Device;
+class Partition;
+class PartResizerWidget;
+
+/**
+ * Synchronize a PartResizerWidget and a QSpinBox
+ */
+class PartitionSizeController : public QObject
+{
+    Q_OBJECT
+public:
+    explicit PartitionSizeController( QObject* parent = nullptr );
+    void setPartResizerWidget( PartResizerWidget* widget );
+    void setSpinBox( QSpinBox* spinBox );
+    void init( Device* device, Partition* partition );
+
+private:
+    PartResizerWidget* m_partResizerWidget = nullptr;
+    QSpinBox* m_spinBox = nullptr;
+    Device* m_device = nullptr;
+    Partition* m_partition = nullptr;
+    bool m_updating = false;
+
+    void updateConnections();
+    void doUpdateSpinBox();
+
+private Q_SLOTS:
+    void updatePartResizerWidget();
+    void updateSpinBox();
+};
+
+#endif /* PARTITIONSIZECONTROLLER_H */