diff --git a/Packages/vChewing_MainAssembly/Sources/MainAssembly/SessionCtl_Core.swift b/Packages/vChewing_MainAssembly/Sources/MainAssembly/SessionCtl_Core.swift
index 3057e293..f8b55b0f 100644
--- a/Packages/vChewing_MainAssembly/Sources/MainAssembly/SessionCtl_Core.swift
+++ b/Packages/vChewing_MainAssembly/Sources/MainAssembly/SessionCtl_Core.swift
@@ -322,6 +322,16 @@ public extension SessionCtl {
       Self.theShiftKeyDetector.toggleWithLShift = PrefMgr.shared.togglingAlphanumericalModeWithLShift
       Self.theShiftKeyDetector.toggleWithRShift = PrefMgr.shared.togglingAlphanumericalModeWithRShift
 
+      if isASCIIMode, !IMEApp.isKeyboardJIS {
+        if #available(macOS 10.15, *) {
+          if !Self.theShiftKeyDetector.enabled {
+            isASCIIMode = false
+          }
+        } else {
+          isASCIIMode = false
+        }
+      }
+
       DispatchQueue.main.async {
         AppDelegate.shared.checkUpdate(forced: false)
         AppDelegate.shared.checkMemoryUsage()