diff --git a/app/ui.js b/app/ui.js
index c5b1f890d..061d48336 100644
--- a/app/ui.js
+++ b/app/ui.js
@@ -50,6 +50,7 @@ import {
     FPS
 } from './constants.js';
 import {encodings} from "../core/encodings.js";
+import { normalizeFrameRate } from "../core/util/frame-rate.js";
 import CodecDetector, {CODEC_VARIANT_NAMES, preferredCodecs} from "../core/codecs";
 import { perfLogger } from '../core/util/performance-logger.js';
 
@@ -1451,6 +1452,7 @@ const UI = {
         if (val === null) {
             val = WebUtil.readSetting(name, defVal);
         }
+        val = UI.sanitizeSetting(name, val);
         WebUtil.setSetting(name, val);
         UI.updateSetting(name);
         return val;
@@ -1458,6 +1460,7 @@ const UI = {
 
     // Set the new value, update and disable form control setting
     forceSetting(name, val, disable=true) {
+        val = UI.sanitizeSetting(name, val);
         WebUtil.setSetting(name, val);
         UI.updateSetting(name);
         if (disable) {
@@ -1497,6 +1500,18 @@ const UI = {
         }
     },
 
+    // Ensure settings stay within supported bounds
+    sanitizeSetting(name, value) {
+        switch (name) {
+            case 'framerate':
+            case 'framerate_image_mode':
+            case 'framerate_streaming_mode':
+                return String(normalizeFrameRate(value, FPS.MIN));
+            default:
+                return value;
+        }
+    },
+
     // Save control setting to cookie
     saveSetting(name) {
         const ctrl = document.getElementById('noVNC_setting_' + name);
@@ -1509,6 +1524,13 @@ const UI = {
         } else {
             val = ctrl.value;
         }
+        const sanitized = UI.sanitizeSetting(name, val);
+        if (sanitized !== val) {
+            if (ctrl && typeof ctrl.value !== 'undefined') {
+                ctrl.value = sanitized;
+            }
+            val = sanitized;
+        }
         WebUtil.writeSetting(name, val);
         Log.Debug("Setting saved '" + name + "=" + val + "'");
         return val;
@@ -1528,8 +1550,12 @@ const UI = {
                 val = true;
             }
         }
-
-        return val;
+        const sanitized = UI.sanitizeSetting(name, val);
+        const currentStr = (val === null || typeof val === 'undefined') ? null : String(val);
+        if (sanitized !== val && sanitized !== currentStr) {
+            WebUtil.writeSetting(name, sanitized);
+        }
+        return sanitized;
     },
 
     getSettingElement(name) {
diff --git a/core/encodings.js b/core/encodings.js
index 4e6c97914..9888b87b2 100644
--- a/core/encodings.js
+++ b/core/encodings.js
@@ -30,8 +30,8 @@ export const encodings = {
     pseudoEncodingCompressLevel9: -247,
     pseudoEncodingCompressLevel0: -256,
 
-    pseudoEncodingFrameRateLevel10: -2048,
-    pseudoEncodingFrameRateLevel60: -1998,
+    pseudoEncodingFrameRateLevel10: -4096,
+    pseudoEncodingFrameRateLevel120: -3986,
     pseudoEncodingMaxVideoResolution: -1997,
     pseudoEncodingVideoScalingLevel0: -1996,
     pseudoEncodingVideoScalingLevel9: -1987,
diff --git a/core/rfb.js b/core/rfb.js
index e088a9ec0..f1d78007e 100644
--- a/core/rfb.js
+++ b/core/rfb.js
@@ -29,6 +29,12 @@ import DES from "./des.js";
 import KeyTable from "./input/keysym.js";
 import XtScancode from "./input/xtscancodes.js";
 import { encodings } from "./encodings.js";
+import {
+    FRAME_RATE_MAX,
+    FRAME_RATE_MIN,
+    frameRateToPseudoEncoding,
+    isValidFrameRate,
+} from "./util/frame-rate.js";
 import { messages } from "./messages.js";
 import { MouseButtonMapper, xvncButtonToMask } from "./mousebuttonmapper.js";
 
@@ -640,8 +646,8 @@ export default class RFB extends EventTargetMixin {
 
     get frameRate() { return this._frameRate; }
     set frameRate(value) {
-        if (!Number.isInteger(value) || value < 1 || value > 120) {
-            Log.Error("frame rate must be an integer between 1 and 120");
+        if (!isValidFrameRate(value)) {
+            Log.Error(`frame rate must be an integer between ${FRAME_RATE_MIN} and ${FRAME_RATE_MAX}`);
             return;
         }
 
@@ -3463,7 +3469,7 @@ export default class RFB extends EventTargetMixin {
         encs.push(encodings.pseudoEncodingVideoTimeLevel0 + this.videoTime);
         encs.push(encodings.pseudoEncodingVideoOutTimeLevel1 + this.videoOutTime - 1);
         encs.push(encodings.pseudoEncodingVideoScalingLevel0 + this.videoScaling);
-        encs.push(encodings.pseudoEncodingFrameRateLevel10 + this.frameRate - 10);
+        encs.push(frameRateToPseudoEncoding(this.frameRate));
         encs.push(encodings.pseudoEncodingMaxVideoResolution);
 
         // Order is important: first options, then streaming mode
diff --git a/core/util/frame-rate.js b/core/util/frame-rate.js
new file mode 100644
index 000000000..16c0361c1
--- /dev/null
+++ b/core/util/frame-rate.js
@@ -0,0 +1,26 @@
+import { encodings } from "../encodings.js";
+
+export const FRAME_RATE_MIN = 10;
+export const FRAME_RATE_MAX = 120;
+
+export function isValidFrameRate(value) {
+    return Number.isInteger(value) &&
+        value >= FRAME_RATE_MIN && value <= FRAME_RATE_MAX;
+}
+
+export function normalizeFrameRate(value, fallback) {
+    const fallbackValue = isValidFrameRate(fallback) ? fallback : FRAME_RATE_MIN;
+    const numericValue = (value === null || value === undefined || value === "") ?
+        fallbackValue : Number(value);
+    const finiteValue = Number.isFinite(numericValue) ? numericValue : fallbackValue;
+
+    return Math.round(Math.max(FRAME_RATE_MIN, Math.min(FRAME_RATE_MAX, finiteValue)));
+}
+
+export function frameRateToPseudoEncoding(value) {
+    if (!isValidFrameRate(value)) {
+        throw new RangeError(`Frame rate must be an integer between ${FRAME_RATE_MIN} and ${FRAME_RATE_MAX}`);
+    }
+
+    return encodings.pseudoEncodingFrameRateLevel10 + value - FRAME_RATE_MIN;
+}
diff --git a/index.html b/index.html
index 4f30332e6..0e16ee859 100644
--- a/index.html
+++ b/index.html
@@ -428,7 +428,7 @@ <h1 class="noVNC_logo">
                                             </li>
                                             <li>
                                                 <label for="noVNC_setting_framerate_image_mode">Frame Rate:</label>
-                                                <input id="noVNC_setting_framerate_image_mode" type="number" min="1" max="120" value="30">
+                                                <input id="noVNC_setting_framerate_image_mode" type="number" min="10" max="120" step="1" value="30">
                                             </li>
                                             <li>
                                                 <label for="noVNC_setting_jpeg_video_quality">Video JPEG Quality:</label>
@@ -509,7 +509,7 @@ <h1 class="noVNC_logo">
                                             </li>
                                             <li>
                                                 <label for="noVNC_setting_framerate_streaming_mode">Frame Rate:</label>
-                                                <input id="noVNC_setting_framerate_streaming_mode" type="number" min="1" max="120" value="30">
+                                                <input id="noVNC_setting_framerate_streaming_mode" type="number" min="10" max="120" step="1" value="30">
                                             </li>
 <!--                                            <li>-->
 <!--                                                <label for="noVNC_setting_preset">Preset:</label>-->