diff --git a/kcms/input/main.cpp b/kcms/input/main.cpp
--- a/kcms/input/main.cpp
+++ b/kcms/input/main.cpp
@@ -21,63 +21,54 @@
  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  */
 
-#include <config-X11.h>
+#include "klauncher_iface.h"
+#include "mouse.h"
 
-#include <kconfig.h>
 #include <QFile>
-
-#include "mouse.h"
 #include <QX11Info>
 
-#include <klauncher_iface.h>
+#include <KConfig>
 
+#include <config-X11.h>
 #include <X11/Xlib.h>
 #ifdef HAVE_XCURSOR
 #  include <X11/Xcursor/Xcursor.h>
 #endif
 
-extern "C"
+extern "C" Q_DECL_EXPORT void kcminit_mouse()
 {
-  Q_DECL_EXPORT void kcminit_mouse()
-  {
-      KConfig *config = new KConfig("kcminputrc", KConfig::NoGlobals );
-
-    Display *dpy = nullptr;
-    const bool platformX11 = QX11Info::isPlatformX11();
-    if (platformX11) {
-        dpy = QX11Info::display();
-    } else {
-        // let's hope we have a compatibility system like Xwayland ready
-        dpy = XOpenDisplay(nullptr);
-    }
+    KConfig config("kcminputrc", KConfig::NoGlobals);
 
     MouseSettings settings;
-    settings.load(config, dpy);
+    settings.load(&config);
     settings.apply(true); // force
 
 #ifdef HAVE_XCURSOR
-    KConfigGroup group = config->group("Mouse");
+    // let's hope we have a compatibility system like Xwayland ready
+    Display *dpy = QX11Info::isPlatformX11() ? QX11Info::display() : XOpenDisplay(nullptr);
+
+    KConfigGroup group = config.group("Mouse");
     QString theme = group.readEntry("cursorTheme", QString());
     QString size = group.readEntry("cursorSize", QString());
 
     // Note: If you update this code, update kapplymousetheme as well.
 
     // use a default value for theme only if it's not configured at all, not even in X resources
-    if( theme.isEmpty()
-        && (!dpy ||
-                (QByteArray( XGetDefault( dpy, "Xcursor", "theme" )).isEmpty()
-                 && QByteArray( XcursorGetTheme( dpy)).isEmpty())))
+    if (theme.isEmpty()
+            && (!dpy ||
+                (QByteArray(XGetDefault(dpy, "Xcursor", "theme")).isEmpty()
+                 && QByteArray(XcursorGetTheme(dpy)).isEmpty())))
     {
         theme = "breeze_cursors";
     }
 
-     // Apply the KDE cursor theme to ourselves
+    // Apply the KDE cursor theme to ourselves
     if (dpy) {
-        if( !theme.isEmpty())
+        if(!theme.isEmpty())
             XcursorSetTheme(dpy, QFile::encodeName(theme));
 
         if (!size.isEmpty())
-            XcursorSetDefaultSize(dpy, size.toUInt());
+            XcursorSetDefaultSize(dpy, size.toInt());
 
         // Load the default cursor from the theme and apply it to the root window.
         Cursor handle = XcursorLibraryLoadCursor(dpy, "left_ptr");
@@ -95,15 +86,9 @@
     if( !size.isEmpty())
         klauncher.setLaunchEnv(QStringLiteral("XCURSOR_SIZE"), size);
 
-#endif
-
-    if (!platformX11) {
+    if (!QX11Info::isPlatformX11()) {
         XFlush(dpy);
         XCloseDisplay(dpy);
     }
-
-    delete config;
-  }
+#endif
 }
-
-
diff --git a/kcms/input/mouse.h b/kcms/input/mouse.h
--- a/kcms/input/mouse.h
+++ b/kcms/input/mouse.h
@@ -28,18 +28,16 @@
  */
 
 
-#ifndef __MOUSECONFIG_H__
-#define __MOUSECONFIG_H__
+#ifndef MOUSECONFIG_H
+#define MOUSECONFIG_H
 
 #include <QX11Info>
 
-#include <config-workspace.h>
+#include <KCModule>
 
-#include <kcmodule.h>
-#include "ui_kmousedlg.h"
+#include "config-workspace.h"
 
-#define RIGHT_HANDED 0
-#define LEFT_HANDED  1
+#include "ui_kmousedlg.h"
 
 class QCheckBox;
 class QDoubleSpinBox;
@@ -50,32 +48,37 @@
 class KMouseDlg : public QWidget, public Ui::KMouseDlg
 {
 public:
-    KMouseDlg( QWidget *parent ) : QWidget( parent ) {
-        setupUi( this );
-    }
+    KMouseDlg(QWidget *parent);
 };
 
 class MouseSettings
 {
 public:
     void save(KConfig *);
-    void load(KConfig *, Display *dpy = QX11Info::display());
+    void load(KConfig *);
     void apply(bool force=false);
 
 public:
+    enum class Handedness : int
+    {
+        Right = 0,
+        Left = 1,
+    };
+
     int num_buttons;
-    int middle_button;
+    unsigned char middle_button;
     bool handedEnabled;
-    bool m_handedNeedsApply;
-    int handed;
+    bool handednessChanged;
+    Handedness handed;
     double accelRate;
     int thresholdMove;
     int doubleClickInterval;
     int dragStartTime;
     int dragStartDist;
     bool singleClick;
     int wheelScrollLines;
     bool reverseScrollPolarity;
+    bool scrollPolarityChanged;
 };
 
 class MouseConfig : public KCModule
@@ -100,11 +103,11 @@
 private:
     double getAccel();
     int getThreshold();
-    int getHandedness();
+    MouseSettings::Handedness getHandedness();
 
     void setAccel(double);
     void setThreshold(int);
-    void setHandedness(int);
+    void setHandedness(MouseSettings::Handedness);
 
     QDoubleSpinBox *accel;
     QSpinBox *thresh;
@@ -127,4 +130,3 @@
 };
 
 #endif
-
diff --git a/kcms/input/mouse.cpp b/kcms/input/mouse.cpp
--- a/kcms/input/mouse.cpp
+++ b/kcms/input/mouse.cpp
@@ -47,42 +47,45 @@
  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  */
 
+#include "mouse.h"
+
+#include "config-workspace.h"
+
+#include <KAboutData>
+#include <KConfig>
+#include <KGlobalSettings>
+#include <KLocalizedString>
+#include <KPluginFactory>
+#include <KPluginLoader>
+#include <KStandardDirs>
+#include <KToolInvocation>
+
 #include <QCheckBox>
 #include <QDoubleSpinBox>
 #include <QFormLayout>
 #include <QSpinBox>
 #include <QWhatsThis>
 #include <QTabWidget>
+#include <QX11Info>
 
-#include <ktoolinvocation.h>
-#include <klocalizedstring.h>
-#include <kconfig.h>
-#include <kstandarddirs.h>
-#include <kaboutdata.h>
-#include <KPluginFactory>
-#include <KPluginLoader>
-
-#include <config-workspace.h>
-
-#include "mouse.h"
-
+#include <evdev-properties.h>
 #include <X11/X.h>
 #include <X11/Xlib.h>
 #include <X11/Xatom.h>
 #include <X11/extensions/XInput2.h>
 #include <X11/Xutil.h>
-#include <kglobalsettings.h>
-#include <QX11Info>
-#include <evdev-properties.h>
 
 #undef Below
 
 #include "../migrationlib/kdelibs4config.h"
 
 K_PLUGIN_FACTORY(MouseConfigFactory,
         registerPlugin<MouseConfig>(); // mouse
         )
-K_EXPORT_PLUGIN(MouseConfigFactory("kcminput"))
+
+KMouseDlg::KMouseDlg(QWidget *parent) : QWidget( parent ) {
+    setupUi( this );
+}
 
 MouseConfig::MouseConfig(QWidget *parent, const QVariantList &args)
   : KCModule(parent, args)
@@ -108,8 +111,8 @@
 
     group = new QButtonGroup(generalTab);
     group->setExclusive(true);
-    group->addButton(generalTab->rightHanded,RIGHT_HANDED);
-    group->addButton(generalTab->leftHanded,LEFT_HANDED);
+    group->addButton(generalTab->rightHanded, static_cast<int>(MouseSettings::Handedness::Right));
+    group->addButton(generalTab->leftHanded,  static_cast<int>(MouseSettings::Handedness::Left));
 
     connect(group, SIGNAL(buttonClicked(int)), this, SLOT(changed()));
     connect(group, SIGNAL(buttonClicked(int)), this, SLOT(slotHandedChanged(int)));
@@ -138,8 +141,8 @@
     connect(generalTab->singleClick, SIGNAL(clicked()), this, SLOT(changed()));
 
     // Only allow setting reversing scroll polarity if we have scroll buttons
-    unsigned char map[20];
-    if (QX11Info::isPlatformX11() && XGetPointerMapping(QX11Info::display(), map, 20) >= 5)
+    unsigned char map[256];
+    if (QX11Info::isPlatformX11() && XGetPointerMapping(QX11Info::display(), map, 256) >= 5)
     {
       generalTab->cbScrollPolarity->setEnabled(true);
       generalTab->cbScrollPolarity->show();
@@ -253,7 +256,13 @@
     dragStartDist->setWhatsThis(wtstr);
 
     wheelScrollLines = new QSpinBox(advancedTab);
-    wheelScrollLines->setRange(1, 12);
+    wheelScrollLines->setRange(0, 12);
+    /*
+     * FIXME: wheelScrollLines = 0 allows user to disable scrolling in Qt/KDE apps,
+     * but not in apps that handle scrolling on their own (e.g. Google Chrome)
+     * which ignore the setting completely.
+     * This requires a separate solution (like changing scrolling distance or unmapping scroll buttons)
+     */
     wheelScrollLines->setSingleStep(1);
     wheelScrollLines->setValue(3);
     wheelScrollLines->setSizePolicy(QSizePolicy::MinimumExpanding, QSizePolicy::Fixed);
@@ -380,28 +389,27 @@
     thresh->setValue(val);
 }
 
-
-int MouseConfig::getHandedness()
+MouseSettings::Handedness MouseConfig::getHandedness()
 {
     if (generalTab->rightHanded->isChecked())
-        return RIGHT_HANDED;
+        return MouseSettings::Handedness::Right;
     else
-        return LEFT_HANDED;
+        return MouseSettings::Handedness::Left;
 }
 
-void MouseConfig::setHandedness(int val)
+void MouseConfig::setHandedness(MouseSettings::Handedness val)
 {
     generalTab->rightHanded->setChecked(false);
     generalTab->leftHanded->setChecked(false);
-    if (val == RIGHT_HANDED) {
+    if (val == MouseSettings::Handedness::Right) {
         generalTab->rightHanded->setChecked(true);
-        generalTab->mousePix->setPixmap(KStandardDirs::locate("data", "kcminput/pics/mouse_rh.png"));
+        generalTab->mousePix->setPixmap(QStandardPaths::locate(QStandardPaths::GenericDataLocation, "kcminput/pics/mouse_rh.png"));
     }
     else {
         generalTab->leftHanded->setChecked(true);
-        generalTab->mousePix->setPixmap(KStandardDirs::locate("data", "kcminput/pics/mouse_lh.png"));
+        generalTab->mousePix->setPixmap(QStandardPaths::locate(QStandardPaths::GenericDataLocation, "kcminput/pics/mouse_lh.png"));
     }
-    settings->m_handedNeedsApply = true;
+    settings->handednessChanged = true;
 }
 
 void MouseConfig::load()
@@ -499,7 +507,7 @@
 {
     setThreshold(2);
     setAccel(2);
-    setHandedness(RIGHT_HANDED);
+    setHandedness(MouseSettings::Handedness::Right);
     generalTab->cbScrollPolarity->setChecked(false);
     doubleClickInterval->setValue(400);
     dragStartTime->setValue(500);
@@ -522,28 +530,30 @@
 /** No descriptions */
 void MouseConfig::slotHandedChanged(int val)
 {
-    if (val==RIGHT_HANDED)
-        generalTab->mousePix->setPixmap(KStandardDirs::locate("data", "kcminput/pics/mouse_rh.png"));
+    if (val == static_cast<int>(MouseSettings::Handedness::Right))
+        generalTab->mousePix->setPixmap(QStandardPaths::locate(QStandardPaths::GenericDataLocation, "kcminput/pics/mouse_rh.png"));
     else
-        generalTab->mousePix->setPixmap(KStandardDirs::locate("data", "kcminput/pics/mouse_lh.png"));
-    settings->m_handedNeedsApply = true;
+        generalTab->mousePix->setPixmap(QStandardPaths::locate(QStandardPaths::GenericDataLocation, "kcminput/pics/mouse_lh.png"));
+    settings->handednessChanged = true;
 }
 
-void MouseSettings::load(KConfig *config, Display *dpy)
+void MouseSettings::load(KConfig *config)
 {
     // TODO: what's a good threshold default value
     int threshold = 0;
-    int h = RIGHT_HANDED;
+    Handedness h = Handedness::Right;
     double accel = 1.0;
     if (QX11Info::isPlatformX11()) {
-        int accel_num, accel_den;
+        auto display = QX11Info::display();
+        int accel_num = 1;
+        int accel_den = 1;
 
-        XGetPointerControl(dpy, &accel_num, &accel_den, &threshold);
-        accel = float(accel_num) / float(accel_den);
+        XGetPointerControl(display, &accel_num, &accel_den, &threshold);
+        accel = static_cast<double>(accel_num) / accel_den;
 
         // get settings from X server
-        unsigned char map[20];
-        num_buttons = XGetPointerMapping(dpy, map, 20);
+        unsigned char map[256];
+        num_buttons = XGetPointerMapping(display, map, 256);
 
         handedEnabled = true;
 
@@ -555,25 +565,25 @@
         }
         else if (num_buttons == 2)
         {
-            if ((int)map[0] == 1 && (int)map[1] == 2)
-                h = RIGHT_HANDED;
-            else if ((int)map[0] == 2 && (int)map[1] == 1)
-                h = LEFT_HANDED;
+            if (map[0] == 1 && map[1] == 2)
+                h = Handedness::Right;
+            else if (map[0] == 2 && map[1] == 1)
+                h = Handedness::Left;
             else
                 /* custom button setup: disable button remapping */
                 handedEnabled = false;
         }
         else
         {
-            middle_button = (int)map[1];
-            if ((int)map[0] == 1 && (int)map[2] == 3)
-            h = RIGHT_HANDED;
-            else if ((int)map[0] == 3 && (int)map[2] == 1)
-            h = LEFT_HANDED;
+            middle_button = map[1];
+            if (map[0] == 1 && map[2] == 3)
+                h = Handedness::Right;
+            else if (map[0] == 3 && map[2] == 1)
+                h = Handedness::Left;
             else
             {
-            /* custom button setup: disable button remapping */
-            handedEnabled = false;
+                /* custom button setup: disable button remapping */
+                handedEnabled = false;
             }
         }
     } else {
@@ -596,16 +606,14 @@
 
     QString key = group.readEntry("MouseButtonMapping");
     if (key == "RightHanded")
-        handed = RIGHT_HANDED;
+        handed = Handedness::Right;
     else if (key == "LeftHanded")
-        handed = LEFT_HANDED;
-#ifdef __GNUC__
-#warning was key == NULL how was this working? is key.isNull() what the coder meant?
-#endif
+        handed = Handedness::Left;
     else if (key.isNull())
         handed = h;
     reverseScrollPolarity = group.readEntry("ReverseScrollPolarity", false);
-    m_handedNeedsApply = false;
+    handednessChanged = false;
+    scrollPolarityChanged = false;
 
     // SC/DC/AutoSelect/ChangeCursor
     group = config->group("KDE");
@@ -637,60 +645,59 @@
     if (!QX11Info::isPlatformX11()) {
         return;
     }
-    XChangePointerControl(QX11Info::display(),
-                          true, true, int(qRound(accelRate*10)), 10, thresholdMove);
+
+    const auto dpy = QX11Info::display();
+    XChangePointerControl(dpy,
+                          true, true, qRound(accelRate*10), 10, thresholdMove);
 
     // 256 might seems extreme, but X has already been known to return 32,
     // and we don't want to truncate things. Xlib limits the table to 256 bytes,
     // so it's a good upper bound..
     unsigned char map[256];
-    num_buttons = XGetPointerMapping(QX11Info::display(), map, 256);
+    num_buttons = XGetPointerMapping(dpy, map, 256);
 
-    int remap=(num_buttons>=1);
-    if (handedEnabled && (m_handedNeedsApply || force)) {
-        if (num_buttons == 1)
-        {
-            map[0] = (unsigned char) 1;
-        }
-        else if (num_buttons == 2)
+    if (num_buttons > 1
+            && handedEnabled
+            && (handednessChanged || force)) {
+        if (num_buttons == 2)
         {
-            if (handed == RIGHT_HANDED)
+            if (handed == Handedness::Right)
             {
-                map[0] = (unsigned char) 1;
-                map[1] = (unsigned char) 3;
+                map[0] = 1;
+                map[1] = 2;
             }
             else
             {
-                map[0] = (unsigned char) 3;
-                map[1] = (unsigned char) 1;
+                map[0] = 2;
+                map[1] = 1;
             }
         }
         else // 3 buttons and more
         {
-            if (handed == RIGHT_HANDED)
+            if (handed == Handedness::Right)
             {
-                map[0] = (unsigned char) 1;
-                map[1] = (unsigned char) middle_button;
-                map[2] = (unsigned char) 3;
+                map[0] = 1;
+                map[1] = middle_button;
+                map[2] = 3;
             }
             else
             {
-                map[0] = (unsigned char) 3;
-                map[1] = (unsigned char) middle_button;
-                map[2] = (unsigned char) 1;
+                map[0] = 3;
+                map[1] = middle_button;
+                map[2] = 1;
             }
         }
 
-        int retval;
-        if (remap) {
-            while ((retval=XSetPointerMapping(QX11Info::display(), map,
-                                              num_buttons)) == MappingBusy)
-              /* keep trying until the pointer is free */
-            { };
-        }
+        while (XSetPointerMapping(dpy, map,
+                                  num_buttons) == MappingBusy)
+            /* keep trying until the pointer is free */
+        { };
+
+        handednessChanged = false;
+    }
 
+    if (scrollPolarityChanged || force) {
         // apply reverseScrollPolarity
-        Display *dpy = QX11Info::display();
         Atom prop_wheel_emulation = XInternAtom(dpy, EVDEV_PROP_WHEEL, True);
         Atom prop_scroll_distance = XInternAtom(dpy, EVDEV_PROP_SCROLL_DISTANCE, True);
         Atom prop_wheel_emulation_axes = XInternAtom(dpy, EVDEV_PROP_WHEEL_AXES, True);
@@ -719,13 +726,13 @@
                 }
 
                 // pointer device without wheel emulation
-                if (type_return != XA_INTEGER || data == NULL || *data == False) {
+                if (type_return != XA_INTEGER || data == nullptr || *data == False) {
                     status = XIGetProperty(dpy, deviceid, prop_scroll_distance, 0, 3,
                                            False, XA_INTEGER, &type_return, &format_return,
                                            &num_items_return, &bytes_after_return, &data2);
                     // negate scroll distance
                     if (status == Success && type_return == XA_INTEGER &&
-                          format_return == 32 && num_items_return == 3) {
+                            format_return == 32 && num_items_return == 3) {
                         int32_t *vals = (int32_t*)data2;
                         for (unsigned long i=0; i<num_items_return; ++i) {
                             int32_t val = *(vals+i);
@@ -739,7 +746,7 @@
                                            False, XA_INTEGER, &type_return, &format_return,
                                            &num_items_return, &bytes_after_return, &data2);
                     if (status == Success && type_return == XA_INTEGER &&
-                          format_return == 8 && num_items_return == 4) {
+                            format_return == 8 && num_items_return == 4) {
                         // when scroll direction is not reversed,
                         // up button id should be smaller than down button id,
                         // up/left are odd elements, down/right are even elements
@@ -756,12 +763,12 @@
                     }
                 }
 
-                if (data != NULL) { XFree(data); }
-                if (data2 != NULL) { XFree(data2); }
+                if (data != nullptr) { XFree(data); }
+                if (data2 != nullptr) { XFree(data2); }
             }
         }
         XIFreeDeviceInfo(info);
-        m_handedNeedsApply = false;
+        scrollPolarityChanged = false;
     }
 }
 
@@ -771,7 +778,7 @@
     KConfigGroup kcminputGroup(kcminputProfile, "Mouse");
     kcminputGroup.writeEntry("Acceleration",accelRate);
     kcminputGroup.writeEntry("Threshold",thresholdMove);
-    if (handed == RIGHT_HANDED)
+    if (handed == Handedness::Right)
         kcminputGroup.writeEntry("MouseButtonMapping",QString("RightHanded"));
     else
         kcminputGroup.writeEntry("MouseButtonMapping",QString("LeftHanded"));
@@ -797,7 +804,7 @@
 
 void MouseConfig::slotScrollPolarityChanged()
 {
-    settings->m_handedNeedsApply = true;
+    settings->scrollPolarityChanged = true;
 }
 
 #include "mouse.moc"