diff --git a/lib/web_ui/lib/src/engine/key_map.g.dart b/lib/web_ui/lib/src/engine/key_map.g.dart
index d02946a8b6726..d4cecae4e6bc0 100644
--- a/lib/web_ui/lib/src/engine/key_map.g.dart
+++ b/lib/web_ui/lib/src/engine/key_map.g.dart
@@ -574,6 +574,7 @@ const Map<String, List<int?>> kWebLogicalLocationMap = <String, List<int?>>{
   '8': <int?>[0x00000000038, null, null, 0x00200000238], // digit8, null, null, numpad8
   '9': <int?>[0x00000000039, null, null, 0x00200000239], // digit9, null, null, numpad9
   'Alt': <int?>[0x00200000104, 0x00200000104, 0x00200000105, null], // altLeft, altLeft, altRight, null
+  'AltGraph': <int?>[0x00100000103, null, 0x00100000103, null], // altGraph, null, altGraph, null
   'ArrowDown': <int?>[0x00100000301, null, null, 0x00200000232], // arrowDown, null, null, numpad2
   'ArrowLeft': <int?>[0x00100000302, null, null, 0x00200000234], // arrowLeft, null, null, numpad4
   'ArrowRight': <int?>[0x00100000303, null, null, 0x00200000236], // arrowRight, null, null, numpad6
diff --git a/lib/web_ui/lib/src/engine/keyboard_binding.dart b/lib/web_ui/lib/src/engine/keyboard_binding.dart
index bb451771adc0c..b5403ac3eedee 100644
--- a/lib/web_ui/lib/src/engine/keyboard_binding.dart
+++ b/lib/web_ui/lib/src/engine/keyboard_binding.dart
@@ -584,7 +584,6 @@ class KeyboardConverter {
       _kPhysicalAltLeft,
       _kPhysicalAltRight,
       _kLogicalAltLeft,
-      _kLogicalAltRight,
       altPressed ? ui.KeyEventType.down : ui.KeyEventType.up,
       eventTimestamp,
     );
@@ -592,7 +591,6 @@ class KeyboardConverter {
       _kPhysicalControlLeft,
       _kPhysicalControlRight,
       _kLogicalControlLeft,
-      _kLogicalControlRight,
       controlPressed ? ui.KeyEventType.down : ui.KeyEventType.up,
       eventTimestamp,
     );
@@ -600,7 +598,6 @@ class KeyboardConverter {
       _kPhysicalMetaLeft,
       _kPhysicalMetaRight,
       _kLogicalMetaLeft,
-      _kLogicalMetaRight,
       metaPressed ? ui.KeyEventType.down : ui.KeyEventType.up,
       eventTimestamp,
     );
@@ -608,7 +605,6 @@ class KeyboardConverter {
       _kPhysicalShiftLeft,
       _kPhysicalShiftRight,
       _kLogicalShiftLeft,
-      _kLogicalShiftRight,
       shiftPressed ? ui.KeyEventType.down : ui.KeyEventType.up,
       eventTimestamp,
     );
@@ -618,7 +614,6 @@ class KeyboardConverter {
     int physicalLeft,
     int physicalRight,
     int logicalLeft,
-    int logicalRight,
     ui.KeyEventType type,
     num domTimestamp,
   ) {
@@ -635,12 +630,14 @@ class KeyboardConverter {
 
     // Synthesize an up event for left key if pressed
     if (synthesizeUp && leftPressed) {
-      _synthesizeKeyUpEvent(domTimestamp, physicalLeft, logicalLeft);
+      final int knownLogicalKey = _pressingRecords[physicalLeft]!;
+      _synthesizeKeyUpEvent(domTimestamp, physicalLeft, knownLogicalKey);
     }
 
     // Synthesize an up event for right key if pressed
     if (synthesizeUp && rightPressed) {
-      _synthesizeKeyUpEvent(domTimestamp, physicalRight, logicalRight);
+      final int knownLogicalKey = _pressingRecords[physicalRight]!;
+      _synthesizeKeyUpEvent(domTimestamp, physicalRight, knownLogicalKey);
     }
   }
 
diff --git a/lib/web_ui/test/engine/pointer_binding_test.dart b/lib/web_ui/test/engine/pointer_binding_test.dart
index 1d3317316a4ab..fd4cca8cab730 100644
--- a/lib/web_ui/test/engine/pointer_binding_test.dart
+++ b/lib/web_ui/test/engine/pointer_binding_test.dart
@@ -760,6 +760,41 @@ void testMain() {
     },
   );
 
+  _testEach<_BasicEventContext>(
+    <_BasicEventContext>[
+      _PointerEventContext(),
+      _MouseEventContext(),
+      _TouchEventContext(),
+    ],
+    'should synthesize modifier keys up event for AltGraph',
+    (_BasicEventContext context) {
+      PointerBinding.instance!.debugOverrideDetector(context);
+
+      final List<ui.KeyData> keyDataList = <ui.KeyData>[];
+      final KeyboardConverter keyboardConverter = createKeyboardConverter(keyDataList);
+      PointerBinding.instance!.debugOverrideKeyboardConverter(keyboardConverter);
+
+      final int physicalAltRight = kWebToPhysicalKey['AltRight']!;
+      final int logicalAltGraph = kWebLogicalLocationMap['AltGraph']![0]!;
+
+      // Simulate pressing `AltGr` key.
+      keyboardConverter.handleEvent(keyDownEvent('AltRight', 'AltGraph'));
+      expect(keyboardConverter.debugKeyIsPressed(physicalAltRight), true);
+      keyDataList.clear(); // Remove key data generated by handleEvent.
+
+      glassPane.dispatchEvent(context.primaryDown());
+      expect(keyDataList.length, 1);
+      expectKeyData(keyDataList.last,
+        type: ui.KeyEventType.up,
+        physical: physicalAltRight,
+        logical: logicalAltGraph,
+        character: null,
+        synthesized: true,
+      );
+      expect(keyboardConverter.debugKeyIsPressed(physicalAltRight), false);
+    },
+  );
+
   _testEach<_ButtonedEventMixin>(
     <_ButtonedEventMixin>[
       if (!isIosSafari) _PointerEventContext(),