diff --git a/src/probers/nsCodingStateMachine.h b/src/probers/nsCodingStateMachine.h
index ac21b2a..1ee6d62 100644
--- a/src/probers/nsCodingStateMachine.h
+++ b/src/probers/nsCodingStateMachine.h
@@ -1,125 +1,130 @@
 /*  -*- C++ -*-
 *  Copyright (C) 1998 <developer@mozilla.org>
 *
 *
 *  Permission is hereby granted, free of charge, to any person obtaining
 *  a copy of this software and associated documentation files (the
 *  "Software"), to deal in the Software without restriction, including
 *  without limitation the rights to use, copy, modify, merge, publish,
 *  distribute, sublicense, and/or sell copies of the Software, and to
 *  permit persons to whom the Software is furnished to do so, subject to
 *  the following conditions:
 *
 *  The above copyright notice and this permission notice shall be included
 *  in all copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 *  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 *  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 *  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 *  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 
 #ifndef nsCodingStateMachine_h__
 #define nsCodingStateMachine_h__
 
 #include "kencodingprober.h"
 
 #include "kcodecs_export.h"
 
 #include "nsPkgInt.h"
 namespace kencodingprober
 {
 typedef enum {
     eStart = 0,
     eError = 1,
     eItsMe = 2
 } nsSMState;
 
 #define GETCLASS(c) GETFROMPCK(((unsigned char)(c)), mModel->classTable)
 
 //state machine model
 typedef struct {
     nsPkgInt classTable;
     unsigned int classFactor;
     nsPkgInt stateTable;
     const unsigned int *charLenTable;
     const char *name;
 } SMModel;
 
 class KCODECS_NO_EXPORT nsCodingStateMachine
 {
 public:
     nsCodingStateMachine(const SMModel *sm)
     {
         mCurrentState = eStart;
         mModel = sm;
     }
     nsSMState NextState(char c)
     {
         //for each byte we get its class KCODECS_NO_EXPORT , if it is first byte, we also get byte length
         unsigned int byteCls = GETCLASS(c);
         if (mCurrentState == eStart) {
             mCurrentBytePos = 0;
             mCurrentCharLen = mModel->charLenTable[byteCls];
         }
         //from byte's class KCODECS_NO_EXPORT and stateTable, we get its next state
-        mCurrentState = (nsSMState)GETFROMPCK(mCurrentState * (mModel->classFactor) + byteCls,
-                                              mModel->stateTable);
+        auto nextCurrentState = GETFROMPCK(mCurrentState * (mModel->classFactor) + byteCls,
+                                                      mModel->stateTable);
+        if (nextCurrentState < eStart || nextCurrentState > eItsMe) {
+            mCurrentState = eError;
+        } else {
+            mCurrentState = static_cast<nsSMState>(nextCurrentState);
+        }
         mCurrentBytePos++;
         return mCurrentState;
     }
     unsigned int  GetCurrentCharLen(void)
     {
         return mCurrentCharLen;
     }
     void      Reset(void)
     {
         mCurrentState = eStart;
     }
     const char *GetCodingStateMachine()
     {
         return mModel->name;
     }
 #ifdef DEBUG_PROBE
     const char *DumpCurrentState()
     {
         switch (mCurrentState) {
         case eStart:
             return "eStart";
         case eError:
             return "eError";
         case eItsMe:
             return "eItsMe";
         default:
             return "OK";
         }
     }
 #endif
 
 protected:
     nsSMState mCurrentState;
     unsigned int mCurrentCharLen;
     unsigned int mCurrentBytePos;
 
     const SMModel *mModel;
 };
 
 extern KCODECS_NO_EXPORT const SMModel UTF8SMModel;
 extern KCODECS_NO_EXPORT const SMModel Big5SMModel;
 extern KCODECS_NO_EXPORT const SMModel EUCJPSMModel;
 extern KCODECS_NO_EXPORT const SMModel EUCKRSMModel;
 extern KCODECS_NO_EXPORT const SMModel GB18030SMModel;
 extern KCODECS_NO_EXPORT const SMModel SJISSMModel;
 extern KCODECS_NO_EXPORT const SMModel UCS2LESMModel;
 extern KCODECS_NO_EXPORT const SMModel UCS2BESMModel;
 
 extern KCODECS_NO_EXPORT const SMModel HZSMModel;
 extern KCODECS_NO_EXPORT const SMModel ISO2022CNSMModel;
 extern KCODECS_NO_EXPORT const SMModel ISO2022JPSMModel;
 extern KCODECS_NO_EXPORT const SMModel ISO2022KRSMModel;
 }
 #endif /* nsCodingStateMachine_h__ */