diff --git a/src/ClipDiff.Windows/Hotkeys/HotKeyGesture.cs b/src/ClipDiff.Windows/Hotkeys/HotKeyGesture.cs
index 031d1b0..022c8f0 100644
--- a/src/ClipDiff.Windows/Hotkeys/HotKeyGesture.cs
+++ b/src/ClipDiff.Windows/Hotkeys/HotKeyGesture.cs
@@ -8,27 +8,37 @@ internal enum HotKeyModifiers : uint
     None = 0,
     Alt = 0x0001,
     Control = 0x0002,
-    Shift = 0x0004,
-    Windows = 0x0008
+    Shift = 0x0004
 }
 
 internal sealed record HotKeyGesture(HotKeyModifiers Modifiers, uint VirtualKey)
 {
+    private const uint VirtualKeyShift = 0x10;
+    private const uint VirtualKeyControl = 0x11;
+    private const uint VirtualKeyMenu = 0x12;
     private const uint VirtualKeyF4 = 0x73;
     private const uint VirtualKeyD = 0x44;
     private const uint VirtualKeyLeftWindows = 0x5B;
     private const uint VirtualKeyRightWindows = 0x5C;
+    private const uint VirtualKeyLeftShift = 0xA0;
+    private const uint VirtualKeyRightShift = 0xA1;
+    private const uint VirtualKeyLeftControl = 0xA2;
+    private const uint VirtualKeyRightControl = 0xA3;
+    private const uint VirtualKeyLeftMenu = 0xA4;
+    private const uint VirtualKeyRightMenu = 0xA5;
+
+    // Win32 calls the Alt key VK_MENU; none of these modifier keys can be a shortcut's primary key.
     private static readonly HashSet<uint> ModifierVirtualKeys =
     [
-        0x10,
-        0x11,
-        0x12,
-        0xA0,
-        0xA1,
-        0xA2,
-        0xA3,
-        0xA4,
-        0xA5
+        VirtualKeyShift,
+        VirtualKeyControl,
+        VirtualKeyMenu,
+        VirtualKeyLeftShift,
+        VirtualKeyRightShift,
+        VirtualKeyLeftControl,
+        VirtualKeyRightControl,
+        VirtualKeyLeftMenu,
+        VirtualKeyRightMenu
     ];
 
     public static HotKeyGesture Default { get; } = new(
@@ -78,10 +88,6 @@ public string DisplayText
                 parts.Add("Shift");
             }
 
-            // If no modifiers and VirtualKey is 0, treat as invalid for display purposes
-            if (parts.Count == 0 && VirtualKey == 0)
-                return "Unassigned";
-
             parts.Add(FormatVirtualKey(VirtualKey));
             return string.Join('+', parts);
         }
diff --git a/tests/ClipDiff.Windows.Tests/HotKeyGestureTests.cs b/tests/ClipDiff.Windows.Tests/HotKeyGestureTests.cs
index e178fc1..7f4da0e 100644
--- a/tests/ClipDiff.Windows.Tests/HotKeyGestureTests.cs
+++ b/tests/ClipDiff.Windows.Tests/HotKeyGestureTests.cs
@@ -28,13 +28,49 @@ public void FormatsTopRowNumpadAndFunctionKeys()
     }
 
     [TestMethod]
-    public void RejectsUnsafeOrIncompleteShortcuts()
+    public void RequiresControlOrAltModifier()
     {
         Assert.IsFalse(new HotKeyGesture(HotKeyModifiers.None, 0x44).IsValid);
         Assert.IsFalse(new HotKeyGesture(HotKeyModifiers.Shift, 0x44).IsValid);
+    }
+
+    [TestMethod]
+    public void EnforcesVirtualKeyBoundaries()
+    {
+        Assert.IsFalse(new HotKeyGesture(HotKeyModifiers.Control, 0).IsValid);
+        Assert.IsTrue(new HotKeyGesture(HotKeyModifiers.Control, 0xFE).IsValid);
+        Assert.IsFalse(new HotKeyGesture(HotKeyModifiers.Control, 0xFF).IsValid);
+    }
+
+    [TestMethod]
+    public void RejectsModifierAsPrimaryKey()
+    {
         Assert.IsFalse(new HotKeyGesture(HotKeyModifiers.Control, 0x11).IsValid);
+    }
+
+    [TestMethod]
+    public void RejectsAltF4()
+    {
         Assert.IsFalse(new HotKeyGesture(HotKeyModifiers.Alt, 0x73).IsValid);
-        Assert.IsFalse(new HotKeyGesture(HotKeyModifiers.Windows, 0x44).IsValid);
+    }
+
+    [TestMethod]
+    public void RejectsUnsupportedModifierFlags()
+    {
+        const HotKeyModifiers unsupportedWindowsModifier = (HotKeyModifiers)0x0008;
+
+        Assert.IsFalse(new HotKeyGesture(unsupportedWindowsModifier, 0x44).IsValid);
+        Assert.IsFalse(
+            new HotKeyGesture(HotKeyModifiers.Control | unsupportedWindowsModifier, 0x44).IsValid);
+    }
+
+    [TestMethod]
+    public void InvalidShortcutsDisplayAsUnassigned()
+    {
+        Assert.AreEqual("Unassigned", new HotKeyGesture(HotKeyModifiers.None, 0x44).DisplayText);
+        Assert.AreEqual("Unassigned", new HotKeyGesture(HotKeyModifiers.Control, 0).DisplayText);
+        Assert.AreEqual("Unassigned", new HotKeyGesture(HotKeyModifiers.Control, 0x11).DisplayText);
+        Assert.AreEqual("Unassigned", new HotKeyGesture(HotKeyModifiers.Alt, 0x73).DisplayText);
     }
 
     [TestMethod]