diff --git a/Packages/vChewing_CandidateWindow/Sources/CandidateWindow/TDKCandidates/CtlCandidateTDK.swift b/Packages/vChewing_CandidateWindow/Sources/CandidateWindow/TDKCandidates/CtlCandidateTDK.swift
index 67ed6c63..6a0f85ac 100644
--- a/Packages/vChewing_CandidateWindow/Sources/CandidateWindow/TDKCandidates/CtlCandidateTDK.swift
+++ b/Packages/vChewing_CandidateWindow/Sources/CandidateWindow/TDKCandidates/CtlCandidateTDK.swift
@@ -202,6 +202,7 @@ public class CtlCandidateTDK: CtlCandidate {
 
   override public func candidateIndexAtKeyLabelIndex(_ id: Int) -> Int {
     let arrCurrentLine = thePool.candidateLines[thePool.currentLineNumber]
+    if !(0..<arrCurrentLine.count).contains(id) { return -114_514 }
     let actualID = max(0, min(id, arrCurrentLine.count - 1))
     return arrCurrentLine[actualID].index
   }
diff --git a/Source/Modules/KeyHandler_HandleCandidate.swift b/Source/Modules/KeyHandler_HandleCandidate.swift
index b722e979..766d3179 100644
--- a/Source/Modules/KeyHandler_HandleCandidate.swift
+++ b/Source/Modules/KeyHandler_HandleCandidate.swift
@@ -242,7 +242,7 @@ extension KeyHandler {
 
     if index != NSNotFound {
       let candidateIndex = ctlCandidate.candidateIndexAtKeyLabelIndex(index)
-      if candidateIndex != Int.max {
+      if candidateIndex != -114_514 {
         delegate?.candidateSelectionCalledByKeyHandler(at: candidateIndex)
         return true
       }
@@ -282,7 +282,7 @@ extension KeyHandler {
 
       if shouldAutoSelectCandidate {
         let candidateIndex = ctlCandidate.candidateIndexAtKeyLabelIndex(0)
-        if candidateIndex != Int.max {
+        if candidateIndex != -114_514 {
           delegate?.candidateSelectionCalledByKeyHandler(at: candidateIndex)
           stateCallback(IMEState.ofAbortion())
           return handle(