diff --git a/binaries/data/mods/mod/gui/common/modern/sprites.xml b/binaries/data/mods/mod/gui/common/modern/sprites.xml
index 40a5a76a5c..b8e05423ac 100644
--- a/binaries/data/mods/mod/gui/common/modern/sprites.xml
+++ b/binaries/data/mods/mod/gui/common/modern/sprites.xml
@@ -193,6 +193,21 @@
 			size = "0 1 100% 100%-1"
 		/>
 	</sprite>
+	<sprite name="ModernDarkBoxWhiteInvalid">
+		<!-- borders -->
+		<image texture = "global/modern/white-separator.png"
+			real_texture_placement = "0 0 806 1"
+			size = "0 0 100% 1"
+		/>
+		<image texture = "global/modern/white-separator.png"
+			real_texture_placement = "0 0 806 1"
+			size = "0 100%-1 100% 100%"
+		/>
+		<!-- background -->
+		<image backcolor = "127 0 0 100"
+			size = "0 1 100% 100%-1"
+		/>
+	</sprite>
 	<sprite name = "ModernDarkBoxGoldNoBottom">
 		<image texture = "global/modern/gold-separator.png"
 			real_texture_placement = "0 0 806 1"
diff --git a/binaries/data/mods/public/gui/options/options.js b/binaries/data/mods/public/gui/options/options.js
index 25b5e381e7..437af4497c 100644
--- a/binaries/data/mods/public/gui/options/options.js
+++ b/binaries/data/mods/public/gui/options/options.js
@@ -51,7 +51,7 @@ var g_DependentLabelIndentation = 25;
  * @property guiToValue - returns the value of the GUI control.
  * @property guiSetter - event name that should be considered a value change of the GUI control.
  * @property initGUI - sets properties of the GUI control that are independent of the current value.
- * @property sanitizeValue - ensures that a given value is in the defined value range.
+ * @property sanitizeValue - Displays a visual clue if the entered value is invalid and returns a sane value.
  * @property tooltip - appends a custom tooltip to the given option description depending on the current value.
  */
 var g_OptionType = {
@@ -75,15 +75,22 @@ var g_OptionType = {
 	},
 	"number":
 	{
-		"configToValue": value => +value,
+		"configToValue": value => value,
 		"valueToGui": (value, control) => {
 			control.caption = value;
 		},
-		"guiToValue": control => +control.caption,
+		"guiToValue": control => control.caption,
 		"guiSetter": "onTextEdit",
-		"sanitizeValue": (value, option) =>
-			Math.min(option.max || Infinity,
-			Math.max(option.min || -Infinity, value)),
+		"sanitizeValue": (value, control, option) => {
+			let sanitized =
+				Math.min(option.max !== undefined ? option.max : +Infinity,
+				Math.max(option.min !== undefined ? option.min : -Infinity,
+					isNaN(+value) ? 0 : value));
+
+			control.sprite = sanitized == value ? "ModernDarkBoxWhite" : "ModernDarkBoxWhiteInvalid";
+
+			return sanitized;
+		},
 		"tooltip": (value, option) =>
 			sprintf(
 				option.min !== undefined && option.max !== undefined ?
@@ -225,15 +232,15 @@ function displayOptions()
 
 		control[optionType.guiSetter] = function() {};
 		optionType.valueToGui(value, control);
+		if (optionType.sanitizeValue)
+			optionType.sanitizeValue(value, control, option);
 
 		control[optionType.guiSetter] = function() {
 
 			let value = optionType.guiToValue(control);
+
 			if (optionType.sanitizeValue)
-			{
-				value = optionType.sanitizeValue(value, option);
-				optionType.valueToGui(value, control);
-			}
+				optionType.sanitizeValue(value, control, option);
 
 			control.tooltip = option.tooltip + (optionType.tooltip ? "\n" + optionType.tooltip(value, option) : "");
 
@@ -318,6 +325,38 @@ function revertChanges()
 }
 
 function saveChanges()
+{
+	for (let category in g_Options)
+		for (let i = 0; i < g_Options[category].options.length; ++i)
+		{
+			let option = g_Options[category].options[i];
+			let optionType = g_OptionType[option.type];
+			if (!optionType.sanitizeValue)
+				continue;
+
+			let control = Engine.GetGUIObjectByName("option_control_" + option.type + "[" + i + "]");
+			let value = optionType.guiToValue(control);
+
+			if (value == optionType.sanitizeValue(value, control, option))
+				continue;
+
+			g_SelectedCategory = category;
+			displayOptions();
+
+			messageBox(
+				500, 200,
+				translate("Some setting values are invalid! Are you sure to save them?"),
+				translate("Warning"),
+				[translate("No"), translate("Yes")],
+				[null, reallySaveChanges]
+			);
+			return;
+		}
+
+	reallySaveChanges()
+}
+
+function reallySaveChanges()
 {
 	Engine.ConfigDB_WriteFile("user", "config/user.cfg");
 	Engine.ConfigDB_SetChanges("user", false);
diff --git a/binaries/data/mods/public/gui/options/options.xml b/binaries/data/mods/public/gui/options/options.xml
index c432eea528..58ec54b041 100644
--- a/binaries/data/mods/public/gui/options/options.xml
+++ b/binaries/data/mods/public/gui/options/options.xml
@@ -18,7 +18,7 @@
 		<!-- Category Tabs -->
 		<object name="tabButtons" type="image" sprite="ModernDarkBoxGold" size="15 16 210 100%-52">
 			<repeat count="15">
-				<object name="tabButton[n]" type="button" sprite="ModernTabButtonVertical" size="0 0 195 30" hidden="true">
+				<object name="tabButton[n]" type="button" size="0 0 195 30" hidden="true">
 					<object type="text" name="tabButtonText[n]" style="ModernLabelText" ghost="true"/>
 				</object>
 			</repeat>