diff --git a/Packages/vChewing_Shared/Package.swift b/Packages/vChewing_Shared/Package.swift
index 41a00364..64cd0752 100644
--- a/Packages/vChewing_Shared/Package.swift
+++ b/Packages/vChewing_Shared/Package.swift
@@ -13,13 +13,15 @@ let package = Package(
     )
   ],
   dependencies: [
-    .package(path: "../vChewing_CocoaExtension")
+    .package(path: "../vChewing_CocoaExtension"),
+    .package(path: "../vChewing_SwiftExtension")
   ],
   targets: [
     .target(
       name: "Shared",
       dependencies: [
-        .product(name: "CocoaExtension", package: "vChewing_CocoaExtension")
+        .product(name: "CocoaExtension", package: "vChewing_CocoaExtension"),
+        .product(name: "SwiftExtension", package: "vChewing_SwiftExtension")
       ]
     )
   ]
diff --git a/Packages/vChewing_Shared/Sources/Shared/Shared.swift b/Packages/vChewing_Shared/Sources/Shared/Shared.swift
index d7ba66e8..2d1e0204 100644
--- a/Packages/vChewing_Shared/Sources/Shared/Shared.swift
+++ b/Packages/vChewing_Shared/Sources/Shared/Shared.swift
@@ -7,6 +7,7 @@
 // requirements defined in MIT License.
 
 import Foundation
+import SwiftExtension
 
 // MARK: - UserDef Snapshot Manager
 
@@ -214,10 +215,10 @@ public enum CandidateKey {
           return NSLocalizedString("There should not be duplicated keys.", comment: "")
         case .tooShort:
           return NSLocalizedString(
-            "Please specify at least 4 candidate keys.", comment: ""
+            "Please specify at least 6 candidate keys.", comment: ""
           )
         case .tooLong:
-          return NSLocalizedString("Maximum 15 candidate keys allowed.", comment: "")
+          return NSLocalizedString("Maximum 9 candidate keys allowed.", comment: "")
       }
     }
   }
@@ -233,10 +234,10 @@ public enum CandidateKey {
     if trimmed.contains(" ") {
       throw CandidateKey.ErrorType.containSpace
     }
-    if trimmed.count < 4 {
+    if trimmed.count < 6 {
       throw CandidateKey.ErrorType.tooShort
     }
-    if trimmed.count > 15 {
+    if trimmed.count > 9 {
       throw CandidateKey.ErrorType.tooLong
     }
     let set = Set(Array(trimmed))
diff --git a/Packages/vChewing_SwiftExtension/Sources/SwiftExtension/SwiftExtension.swift b/Packages/vChewing_SwiftExtension/Sources/SwiftExtension/SwiftExtension.swift
index 6677a294..f32b21a6 100644
--- a/Packages/vChewing_SwiftExtension/Sources/SwiftExtension/SwiftExtension.swift
+++ b/Packages/vChewing_SwiftExtension/Sources/SwiftExtension/SwiftExtension.swift
@@ -13,7 +13,7 @@ import Foundation
 // Extend the RangeReplaceableCollection to allow it clean duplicated characters.
 // Ref: https://stackoverflow.com/questions/25738817/
 extension RangeReplaceableCollection where Element: Hashable {
-  public var deduplicate: Self {
+  public var deduplicated: Self {
     var set = Set<Element>()
     return filter { set.insert($0).inserted }
   }
diff --git a/Source/Modules/KeyHandler_Core.swift b/Source/Modules/KeyHandler_Core.swift
index 4145ba92..e5a5ab68 100644
--- a/Source/Modules/KeyHandler_Core.swift
+++ b/Source/Modules/KeyHandler_Core.swift
@@ -275,7 +275,7 @@ public class KeyHandler {
       Megrez.Compositor.KeyValuePaired(key: $0.0, value: $0.1.value)
     }
     arrCandidates = arrSuggestedCandidates.filter { arrCandidates.contains($0) } + arrCandidates
-    arrCandidates = arrCandidates.deduplicate
+    arrCandidates = arrCandidates.deduplicated
     arrCandidates = arrCandidates.stableSort { $0.key.split(separator: "-").count > $1.key.split(separator: "-").count }
     return arrCandidates.map { ($0.key, $0.value) }
   }
diff --git a/Source/Modules/PrefMgr_Core.swift b/Source/Modules/PrefMgr_Core.swift
index 47051530..e279d741 100644
--- a/Source/Modules/PrefMgr_Core.swift
+++ b/Source/Modules/PrefMgr_Core.swift
@@ -233,7 +233,10 @@ public class PrefMgr: PrefMgrProtocol {
   @AppProperty(key: UserDef.kCandidateKeys.rawValue, defaultValue: kDefaultCandidateKeys)
   public var candidateKeys: String {
     didSet {
-      if useIMKCandidateWindow {
+      if candidateKeys != candidateKeys.deduplicated {
+        candidateKeys = candidateKeys.deduplicated
+      }
+      if !(6...9).contains(candidateKeys.count) {
         candidateKeys = Self.kDefaultCandidateKeys
       }
     }
diff --git a/Source/Modules/PrefMgr_Extension.swift b/Source/Modules/PrefMgr_Extension.swift
index 5f52af93..9595bf63 100644
--- a/Source/Modules/PrefMgr_Extension.swift
+++ b/Source/Modules/PrefMgr_Extension.swift
@@ -22,6 +22,8 @@ extension PrefMgr {
       disableShiftTogglingAlphanumericalMode = false
       togglingAlphanumericalModeWithLShift = false
     }
+    // 自動糾正選字鍵 (利用其 didSet 特性)
+    candidateKeys = candidateKeys
     // 客體黑名單自動排序去重複。
     clientsIMKTextInputIncapable = Array(Set(clientsIMKTextInputIncapable)).sorted()
     // 注拼槽注音排列選項糾錯。
diff --git a/Source/Modules/UIModules/PrefUI/suiPrefPaneKeyboard.swift b/Source/Modules/UIModules/PrefUI/suiPrefPaneKeyboard.swift
index db5b8442..f0009d3d 100644
--- a/Source/Modules/UIModules/PrefUI/suiPrefPaneKeyboard.swift
+++ b/Source/Modules/UIModules/PrefUI/suiPrefPaneKeyboard.swift
@@ -56,7 +56,7 @@ struct suiPrefPaneKeyboard: View {
             items: CandidateKey.suggestions,
             text: $selSelectionKeys.onChange {
               let value = selSelectionKeys
-              let keys: String = value.trimmingCharacters(in: .whitespacesAndNewlines).deduplicate
+              let keys: String = value.trimmingCharacters(in: .whitespacesAndNewlines).deduplicated
               do {
                 try CandidateKey.validate(keys: keys)
                 PrefMgr.shared.candidateKeys = keys
@@ -64,8 +64,8 @@ struct suiPrefPaneKeyboard: View {
               } catch CandidateKey.ErrorType.empty {
                 selSelectionKeys = PrefMgr.shared.candidateKeys
               } catch {
-                if let window = ctlPrefUI.shared.controller.window {
-                  let alert = NSAlert(error: error)
+                if let window = ctlPrefUI.shared.controller.window, let error = error as? CandidateKey.ErrorType {
+                  let alert = NSAlert(error: error.errorDescription)
                   alert.beginSheetModal(for: window) { _ in
                     selSelectionKeys = PrefMgr.shared.candidateKeys
                   }
diff --git a/Source/Modules/WindowControllers/ctlPrefWindow.swift b/Source/Modules/WindowControllers/ctlPrefWindow.swift
index 0272d84e..17afd11f 100644
--- a/Source/Modules/WindowControllers/ctlPrefWindow.swift
+++ b/Source/Modules/WindowControllers/ctlPrefWindow.swift
@@ -135,7 +135,9 @@ class ctlPrefWindow: NSWindowController {
     }
 
     selectionKeyComboBox.stringValue = candidateSelectionKeys
-    selectionKeyComboBox.isEnabled = false  // 無法與 IMKCandidates 協作，故禁用。
+    if PrefMgr.shared.useIMKCandidateWindow {
+      selectionKeyComboBox.isEnabled = false  // 無法與 IMKCandidates 協作，故禁用。
+    }
   }
 
   // 這裡有必要加上這段處理，用來確保藉由偏好設定介面動過的 CNS 開關能夠立刻生效。
@@ -198,7 +200,7 @@ class ctlPrefWindow: NSWindowController {
       let keys = (sender as AnyObject).stringValue?.trimmingCharacters(
         in: .whitespacesAndNewlines
       )
-      .deduplicate
+      .deduplicated
     else {
       return
     }
@@ -209,8 +211,8 @@ class ctlPrefWindow: NSWindowController {
     } catch CandidateKey.ErrorType.empty {
       selectionKeyComboBox.stringValue = PrefMgr.shared.candidateKeys
     } catch {
-      if let window = window {
-        let alert = NSAlert(error: error)
+      if let window = window, let error = error as? CandidateKey.ErrorType {
+        let alert = NSAlert(error: error.errorDescription)
         alert.beginSheetModal(for: window) { _ in
           self.selectionKeyComboBox.stringValue = PrefMgr.shared.candidateKeys
         }
diff --git a/Source/Resources/Base.lproj/Localizable.strings b/Source/Resources/Base.lproj/Localizable.strings
index c31aa78e..808e721c 100644
--- a/Source/Resources/Base.lproj/Localizable.strings
+++ b/Source/Resources/Base.lproj/Localizable.strings
@@ -51,12 +51,11 @@
 "\"%@\" already exists:\n ENTER to boost, SHIFT+COMMAND+ENTER to nerf, \n BackSpace or Delete key to exclude." = "\"%@\" already exists:\n ENTER to boost, SHIFT+COMMAND+ENTER to nerf, \n BackSpace or Delete key to exclude.";
 "Edit Phrase Replacement Table…" = "Edit Phrase Replacement Table…";
 "Use Phrase Replacement" = "Use Phrase Replacement";
-"Candidates keys cannot be empty." = "Candidates keys cannot be empty.";
 "Candidate keys can only contain ASCII characters like alphanumericals." = "Candidate keys can only contain ASCII characters like alphanumericals.";
 "Candidate keys cannot contain space." = "Candidate keys cannot contain space.";
 "There should not be duplicated keys." = "There should not be duplicated keys.";
-"Please specify at least 4 candidate keys." = "Please specify at least 4 candidate keys.";
-"Maximum 15 candidate keys allowed." = "Maximum 15 candidate keys allowed.";
+"Please specify at least 6 candidate keys." = "Please specify at least 6 candidate keys.";
+"Maximum 9 candidate keys allowed." = "Maximum 9 candidate keys allowed.";
 "⚠︎ Phrase replacement mode enabled, interfering user phrase entry." = "⚠︎ Phrase replacement mode enabled, interfering user phrase entry.";
 "⚠︎ Unhandlable: Chars and Readings in buffer doesn't match." = "⚠︎ Unhandlable: Chars and Readings in buffer doesn't match.";
 "Per-Char Select Mode" = "Per-Char Select Mode";
diff --git a/Source/Resources/en.lproj/Localizable.strings b/Source/Resources/en.lproj/Localizable.strings
index c31aa78e..808e721c 100644
--- a/Source/Resources/en.lproj/Localizable.strings
+++ b/Source/Resources/en.lproj/Localizable.strings
@@ -51,12 +51,11 @@
 "\"%@\" already exists:\n ENTER to boost, SHIFT+COMMAND+ENTER to nerf, \n BackSpace or Delete key to exclude." = "\"%@\" already exists:\n ENTER to boost, SHIFT+COMMAND+ENTER to nerf, \n BackSpace or Delete key to exclude.";
 "Edit Phrase Replacement Table…" = "Edit Phrase Replacement Table…";
 "Use Phrase Replacement" = "Use Phrase Replacement";
-"Candidates keys cannot be empty." = "Candidates keys cannot be empty.";
 "Candidate keys can only contain ASCII characters like alphanumericals." = "Candidate keys can only contain ASCII characters like alphanumericals.";
 "Candidate keys cannot contain space." = "Candidate keys cannot contain space.";
 "There should not be duplicated keys." = "There should not be duplicated keys.";
-"Please specify at least 4 candidate keys." = "Please specify at least 4 candidate keys.";
-"Maximum 15 candidate keys allowed." = "Maximum 15 candidate keys allowed.";
+"Please specify at least 6 candidate keys." = "Please specify at least 6 candidate keys.";
+"Maximum 9 candidate keys allowed." = "Maximum 9 candidate keys allowed.";
 "⚠︎ Phrase replacement mode enabled, interfering user phrase entry." = "⚠︎ Phrase replacement mode enabled, interfering user phrase entry.";
 "⚠︎ Unhandlable: Chars and Readings in buffer doesn't match." = "⚠︎ Unhandlable: Chars and Readings in buffer doesn't match.";
 "Per-Char Select Mode" = "Per-Char Select Mode";
diff --git a/Source/Resources/ja.lproj/Localizable.strings b/Source/Resources/ja.lproj/Localizable.strings
index 40cf9a33..2e18414b 100644
--- a/Source/Resources/ja.lproj/Localizable.strings
+++ b/Source/Resources/ja.lproj/Localizable.strings
@@ -51,12 +51,11 @@
 "\"%@\" already exists:\n ENTER to boost, SHIFT+COMMAND+ENTER to nerf, \n BackSpace or Delete key to exclude." = "「%@」は既存語彙：\n　ENTER で最優先にし、SHIFT+COMMAND+ENTER で優先順位を下げる；\n　BackSpace 或いは Delete で排除。";
 "Edit Phrase Replacement Table…" = "言葉置換表を編集…";
 "Use Phrase Replacement" = "言葉置換機能";
-"Candidates keys cannot be empty." = "言選り用キー陣列に何かキーをご登録ください。";
 "Candidate keys can only contain ASCII characters like alphanumericals." = "言選り用キー陣列にはASCII文字だけをご登録ください（英数など）。";
 "Candidate keys cannot contain space." = "言選り用キー陣列にスペースキーは登録できません。";
 "There should not be duplicated keys." = "言選り用キー陣列に同じキーの重複登録はできません。";
-"Please specify at least 4 candidate keys." = "言選り用キー陣列に少なくとも４つのキーをご登録ください。";
-"Maximum 15 candidate keys allowed." = "言選り用キー陣列には最多１５つキー登録できます。";
+"Please specify at least 6 candidate keys." = "言選り用キー陣列に少なくとも６つのキーをご登録ください。";
+"Maximum 9 candidate keys allowed." = "言選り用キー陣列には最多９つキー登録できます。";
 "⚠︎ Phrase replacement mode enabled, interfering user phrase entry." = "⚠︎ 言葉置換機能稼働中、新添付言葉にも影響。";
 "⚠︎ Unhandlable: Chars and Readings in buffer doesn't match." = "⚠︎ 対処不可：緩衝列の字数は読みの数と不同等。";
 "Per-Char Select Mode" = "全候補入力モード";
diff --git a/Source/Resources/zh-Hans.lproj/Localizable.strings b/Source/Resources/zh-Hans.lproj/Localizable.strings
index 6bda81d9..23a94622 100644
--- a/Source/Resources/zh-Hans.lproj/Localizable.strings
+++ b/Source/Resources/zh-Hans.lproj/Localizable.strings
@@ -51,12 +51,11 @@
 "\"%@\" already exists:\n ENTER to boost, SHIFT+COMMAND+ENTER to nerf, \n BackSpace or Delete key to exclude." = "「%@」已存在：\n　敲 Enter 以升权、敲 Shift+Command+Enter 以降权；\n　敲 BackSpace 或 Delete 以排除。";
 "Edit Phrase Replacement Table…" = "编辑语汇置换表…";
 "Use Phrase Replacement" = "使用语汇置换";
-"Candidates keys cannot be empty." = "您必须指定选字键。";
 "Candidate keys can only contain ASCII characters like alphanumericals." = "选字键只能是英数等 ASCII 字符。";
 "Candidate keys cannot contain space." = "选字键不得包含空格。";
 "There should not be duplicated keys." = "选字键不得重复。";
-"Please specify at least 4 candidate keys." = "请至少指定四个选字键。";
-"Maximum 15 candidate keys allowed." = "选字键最多只能指定十五个。";
+"Please specify at least 6 candidate keys." = "请至少指定 6 个选字键。";
+"Maximum 9 candidate keys allowed." = "选字键最多只能指定 9 个。";
 "⚠︎ Phrase replacement mode enabled, interfering user phrase entry." = "⚠︎ 语汇置换功能已启用，会波及语汇自订。";
 "⚠︎ Unhandlable: Chars and Readings in buffer doesn't match." = "⚠︎ 无法处理：组字区字数与读音数不对应。";
 "Per-Char Select Mode" = "模拟逐字选字输入";
diff --git a/Source/Resources/zh-Hant.lproj/Localizable.strings b/Source/Resources/zh-Hant.lproj/Localizable.strings
index c5adcb9e..a7e73c72 100644
--- a/Source/Resources/zh-Hant.lproj/Localizable.strings
+++ b/Source/Resources/zh-Hant.lproj/Localizable.strings
@@ -51,12 +51,11 @@
 "\"%@\" already exists:\n ENTER to boost, SHIFT+COMMAND+ENTER to nerf, \n BackSpace or Delete key to exclude." = "「%@」已存在：\n　敲 Enter 以升權、敲 Shift+Command+Enter 以降權；\n　敲 BackSpace 或 Delete 以排除。";
 "Edit Phrase Replacement Table…" = "編輯語彙置換表…";
 "Use Phrase Replacement" = "使用語彙置換";
-"Candidates keys cannot be empty." = "您必須指定選字鍵。";
 "Candidate keys can only contain ASCII characters like alphanumericals." = "選字鍵只能是英數等 ASCII 字符。";
 "Candidate keys cannot contain space." = "選字鍵不得包含空格。";
 "There should not be duplicated keys." = "選字鍵不得重複。";
-"Please specify at least 4 candidate keys." = "請至少指定四個選字鍵。";
-"Maximum 15 candidate keys allowed." = "選字鍵最多只能指定十五個。";
+"Please specify at least 6 candidate keys." = "請至少指定 6 個選字鍵。";
+"Maximum 9 candidate keys allowed." = "選字鍵最多只能指定 9 個。";
 "⚠︎ Phrase replacement mode enabled, interfering user phrase entry." = "⚠︎ 語彙置換功能已啟用，會波及語彙自訂。";
 "⚠︎ Unhandlable: Chars and Readings in buffer doesn't match." = "⚠︎ 無法處理：組字區字數與讀音數不對應。";
 "Per-Char Select Mode" = "模擬逐字選字輸入";