diff --git a/Packages/vChewing_CocoaExtension/Sources/CocoaExtension/CocoaExtension_Misc.swift b/Packages/vChewing_CocoaExtension/Sources/CocoaExtension/CocoaExtension_Misc.swift
index 8a8bbe10..dfa2b988 100644
--- a/Packages/vChewing_CocoaExtension/Sources/CocoaExtension/CocoaExtension_Misc.swift
+++ b/Packages/vChewing_CocoaExtension/Sources/CocoaExtension/CocoaExtension_Misc.swift
@@ -134,6 +134,19 @@ public extension NSApplication {
   }
 }
 
+// MARK: - String.applyingTransform
+
+public extension String {
+  func applyingTransformFW2HW(reverse: Bool) -> String {
+    if #available(macOS 10.11, *) {
+      return applyingTransform(.fullwidthToHalfwidth, reverse: reverse) ?? self
+    }
+    let theString = NSMutableString(string: self)
+    CFStringTransform(theString, nil, kCFStringTransformFullwidthHalfwidth, reverse)
+    return theString as String
+  }
+}
+
 // MARK: - Check whether current date is the given date.
 
 public extension Date {
diff --git a/Source/Modules/InputHandler_HandleInput.swift b/Source/Modules/InputHandler_HandleInput.swift
index 7b3f5db8..57636c25 100644
--- a/Source/Modules/InputHandler_HandleInput.swift
+++ b/Source/Modules/InputHandler_HandleInput.swift
@@ -235,8 +235,7 @@ extension InputHandler {
     if state.type == .ofEmpty {
       if input.isMainAreaNumKey, input.modifierFlags == [.shift, .option] {
         guard let strRAW = input.mainAreaNumKeyChar else { return false }
-        let newString =
-          strRAW.applyingTransform(.fullwidthToHalfwidth, reverse: !prefs.halfWidthPunctuationEnabled) ?? strRAW
+        let newString = strRAW.applyingTransformFW2HW(reverse: !prefs.halfWidthPunctuationEnabled)
         delegate.switchState(IMEState.ofCommitting(textToCommit: newString))
         return true
       }
diff --git a/Source/Modules/SessionCtl_HandleEvent.swift b/Source/Modules/SessionCtl_HandleEvent.swift
index b485d95a..ba1948e7 100644
--- a/Source/Modules/SessionCtl_HandleEvent.swift
+++ b/Source/Modules/SessionCtl_HandleEvent.swift
@@ -130,7 +130,7 @@ public extension SessionCtl {
 
     // Apple 數字小鍵盤處理
     if eventToDeal.isNumericPadKey,
-       let eventCharConverted = eventToDeal.characters?.applyingTransform(.fullwidthToHalfwidth, reverse: false)
+       let eventCharConverted = eventToDeal.characters?.applyingTransformFW2HW(reverse: false)
     {
       eventToDeal = eventToDeal.reinitiate(characters: eventCharConverted) ?? eventToDeal
     }