diff --git a/app/ui.js b/app/ui.js
index 21c2bd80..206018ab 100644
--- a/app/ui.js
+++ b/app/ui.js
@@ -41,6 +41,7 @@ import KeyTable from "../core/input/keysym.js";
 import keysyms from "../core/input/keysymdef.js";
 import Keyboard from "../core/input/keyboard.js";
 import RFB from "../core/rfb.js";
+import { MouseButtonMapper, XVNC_BUTTONS } from "../core/mousebuttonmapper.js";
 import * as WebUtil from "./webutil.js";
 
 const PAGE_TITLE = "KasmVNC";
@@ -264,6 +265,24 @@ const UI = {
         UI.setupSettingLabels();
         UI.updateQuality();
     },
+    initMouseButtonMapper() {
+        const mouseButtonMapper = new MouseButtonMapper();
+
+        const settings = WebUtil.readSetting("mouseButtonMapper");
+        if (settings) {
+            mouseButtonMapper.load(settings);
+            return mouseButtonMapper;
+        }
+
+        mouseButtonMapper.set(0, XVNC_BUTTONS.LEFT_BUTTON);
+        mouseButtonMapper.set(1, XVNC_BUTTONS.MIDDLE_BUTTON);
+        mouseButtonMapper.set(2, XVNC_BUTTONS.RIGHT_BUTTON);
+        mouseButtonMapper.set(3, XVNC_BUTTONS.BACK_BUTTON);
+        mouseButtonMapper.set(4, XVNC_BUTTONS.FORWARD_BUTTON);
+        WebUtil.writeSetting("mouseButtonMapper", mouseButtonMapper.dump());
+
+        return mouseButtonMapper;
+    },
     // Adds a link to the label elements on the corresponding input elements
     setupSettingLabels() {
         const labels = document.getElementsByTagName('LABEL');
@@ -1381,6 +1400,7 @@ const UI = {
         UI.rfb.keyboard.enableIME = UI.getSetting('enable_ime');
         UI.rfb.clipboardBinary = supportsBinaryClipboard() && UI.rfb.clipboardSeamless;
         UI.rfb.enableWebRTC = UI.getSetting('enable_webrtc');
+        UI.rfb.mouseButtonMapper = UI.initMouseButtonMapper();
 
         //Only explicitly request permission to clipboard on browsers that support binary clipboard access
         if (supportsBinaryClipboard()) {
diff --git a/core/mousebuttonmapper.js b/core/mousebuttonmapper.js
new file mode 100644
index 00000000..b69475a4
--- /dev/null
+++ b/core/mousebuttonmapper.js
@@ -0,0 +1,67 @@
+export const XVNC_BUTTONS = {
+    LEFT_BUTTON: 1,
+    MIDDLE_BUTTON: 2,
+    RIGHT_BUTTON: 3,
+    TURN_SCROLL_WHEEL_UP: 4,
+    TURN_SCROLL_WHEEL_DOWN: 5,
+    PUSH_SCROLL_WHEEL_LEFT: 6,
+    PUSH_SCROLL_WHEEL_RIGHT: 7,
+    BACK_BUTTON: 8,
+    FORWARD_BUTTON: 9
+};
+
+export function xvncButtonToMask(xvncButton) {
+    return 1 << (xvncButton - 1);
+}
+
+export default class MouseButtonMapper {
+    constructor() {
+        this.map = new Map();
+    }
+
+    get(mouseButton) {
+        if (!this.map.has(mouseButton)) {
+            return mouseButton;
+        }
+
+        return this.map.get(mouseButton);
+    }
+
+    set(mouseButton, xorgMouseButton) {
+        return this.map.set(mouseButton, xorgMouseButton);
+    }
+
+    delete(mouseButton) {
+        return this.map.delete(mouseButton);
+    }
+
+    dump() {
+        return JSON.stringify(this.map, this._replacer);
+    }
+
+    load(json) {
+        this.map = JSON.parse(json, this._reviver);
+    }
+
+    _replacer(key, value) {
+        if (!(value instanceof Map)) {
+            return value;
+        }
+
+        return {
+            dataType: 'Map',
+            value: Array.from(value.entries())
+        };
+    }
+
+    _reviver(key, value) {
+        if (typeof value === 'object' && value !== null) {
+            if (value.dataType === 'Map') {
+                return new Map(value.value);
+            }
+        }
+        return value;
+    }
+}
+
+export { MouseButtonMapper };
diff --git a/core/rfb.js b/core/rfb.js
index cec38580..18f788eb 100644
--- a/core/rfb.js
+++ b/core/rfb.js
@@ -26,6 +26,7 @@ import DES from "./des.js";
 import KeyTable from "./input/keysym.js";
 import XtScancode from "./input/xtscancodes.js";
 import { encodings } from "./encodings.js";
+import { MouseButtonMapper, xvncButtonToMask } from "./mousebuttonmapper.js";
 
 import RawDecoder from "./decoders/raw.js";
 import CopyRectDecoder from "./decoders/copyrect.js";
@@ -192,6 +193,7 @@ export default class RFB extends EventTargetMixin {
         this._viewportHasMoved = false;
         this._accumulatedWheelDeltaX = 0;
         this._accumulatedWheelDeltaY = 0;
+        this.mouseButtonMapper = null;
 
         // Gesture state
         this._gestureLastTapTime = null;
@@ -1558,6 +1560,7 @@ export default class RFB extends EventTargetMixin {
                                   this._canvas);
         }
 
+        const mappedButton = this.mouseButtonMapper.get(ev.button);
         switch (ev.type) {
             case 'mousedown':
                 setCapture(this._canvas);
@@ -1575,11 +1578,11 @@ export default class RFB extends EventTargetMixin {
                 this.checkLocalClipboard();
 
                 this._handleMouseButton(pos.x, pos.y,
-                                        true, 1 << ev.button);
+                                        true, xvncButtonToMask(mappedButton));
                 break;
             case 'mouseup':
                 this._handleMouseButton(pos.x, pos.y,
-                                        false, 1 << ev.button);
+                                        false, xvncButtonToMask(mappedButton));
                 break;
             case 'mousemove':
                 this._handleMouseMove(pos.x, pos.y);
@@ -3659,21 +3662,22 @@ RFB.messages = {
 
         buff[offset] = 5; // msg-type
 
-        buff[offset + 1] = mask;
+        buff[offset + 1] = mask >> 8;
+        buff[offset + 2] = mask;
 
-        buff[offset + 2] = x >> 8;
-        buff[offset + 3] = x;
+        buff[offset + 3] = x >> 8;
+        buff[offset + 4] = x;
 
-        buff[offset + 4] = y >> 8;
-        buff[offset + 5] = y;
+        buff[offset + 5] = y >> 8;
+        buff[offset + 6] = y;
 
-        buff[offset + 6] = dX >> 8;
-        buff[offset + 7] = dX;
+        buff[offset + 7] = dX >> 8;
+        buff[offset + 8] = dX;
 
-        buff[offset + 8] = dY >> 8;
-        buff[offset + 9] = dY;
+        buff[offset + 9] = dY >> 8;
+        buff[offset + 10] = dY;
 
-        sock._sQlen += 10;
+        sock._sQlen += 11;
         sock.flush();
     },