diff --git a/Packages/vChewing_Shared/Sources/Shared/Protocols/InputSignalProtocol.swift b/Packages/vChewing_Shared/Sources/Shared/Protocols/InputSignalProtocol.swift
index c77bf48b..1eada955 100644
--- a/Packages/vChewing_Shared/Sources/Shared/Protocols/InputSignalProtocol.swift
+++ b/Packages/vChewing_Shared/Sources/Shared/Protocols/InputSignalProtocol.swift
@@ -14,6 +14,7 @@ extension NSEvent: InputSignalProtocol {}
 // MARK: - InputSignalProtocol
 
 public protocol InputSignalProtocol {
+  var modifierFlags: NSEvent.ModifierFlags { get }
   var isTypingVertical: Bool { get }
   var text: String { get }
   var inputTextIgnoringModifiers: String? { get }
diff --git a/Source/Modules/KeyHandler_HandleInput.swift b/Source/Modules/KeyHandler_HandleInput.swift
index 1026d7ef..20c0428c 100644
--- a/Source/Modules/KeyHandler_HandleInput.swift
+++ b/Source/Modules/KeyHandler_HandleInput.swift
@@ -318,14 +318,12 @@ extension KeyHandler {
     // MARK: 全形/半形阿拉伯數字輸入 (FW / HW Arabic Numbers Input)
 
     if state.type == .ofEmpty {
-      if input.isMainAreaNumKey, input.isShiftHold, input.isOptionHold, !input.isControlHold, !input.isCommandHold {
-        // NOTE: 將來棄用 macOS 10.11 El Capitan 支援的時候，把這裡由 CFStringTransform 改為 StringTransform:
-        // https://developer.apple.com/documentation/foundation/stringtransform
+      if input.isMainAreaNumKey, input.modifierFlags == [.shift, .option] {
         guard let stringRAW = input.mainAreaNumKeyChar else { return false }
-        let string = NSMutableString(string: stringRAW)
-        CFStringTransform(string, nil, kCFStringTransformFullwidthHalfwidth, true)
+        let newStringFW = stringRAW.applyingTransform(.fullwidthToHalfwidth, reverse: true) ?? stringRAW
+        let newStringHW = stringRAW.applyingTransform(.fullwidthToHalfwidth, reverse: false) ?? stringRAW
         stateCallback(
-          IMEState.ofCommitting(textToCommit: prefs.halfWidthPunctuationEnabled ? stringRAW : string as String)
+          IMEState.ofCommitting(textToCommit: prefs.halfWidthPunctuationEnabled ? newStringHW : newStringFW)
         )
         stateCallback(IMEState.ofEmpty())
         return true