diff --git a/src/probers/nsBig5Prober.cpp b/src/probers/nsBig5Prober.cpp
index 64f2dfc..aa74524 100644
--- a/src/probers/nsBig5Prober.cpp
+++ b/src/probers/nsBig5Prober.cpp
@@ -1,79 +1,82 @@
 /*  -*- 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.
 */
 
 #include "nsBig5Prober.h"
 
 namespace kencodingprober
 {
 void  nsBig5Prober::Reset(void)
 {
     mCodingSM->Reset();
     mState = eDetecting;
     mDistributionAnalyser.Reset();
 }
 
 nsProbingState nsBig5Prober::HandleData(const char *aBuf, unsigned int aLen)
 {
+    if (aLen == 0)
+        return mState;
+
     nsSMState codingState;
 
     for (unsigned int i = 0; i < aLen; i++) {
         codingState = mCodingSM->NextState(aBuf[i]);
         if (codingState == eError) {
             mState = eNotMe;
             break;
         }
         if (codingState == eItsMe) {
             mState = eFoundIt;
             break;
         }
         if (codingState == eStart) {
             unsigned int charLen = mCodingSM->GetCurrentCharLen();
 
             if (i == 0) {
                 mLastChar[1] = aBuf[0];
                 mDistributionAnalyser.HandleOneChar(mLastChar, charLen);
             } else {
                 mDistributionAnalyser.HandleOneChar(aBuf + i - 1, charLen);
             }
         }
     }
 
     mLastChar[0] = aBuf[aLen - 1];
 
     if (mState == eDetecting)
         if (mDistributionAnalyser.GotEnoughData() && GetConfidence() > SHORTCUT_THRESHOLD) {
             mState = eFoundIt;
         }
 
     return mState;
 }
 
 float nsBig5Prober::GetConfidence(void)
 {
     float distribCf = mDistributionAnalyser.GetConfidence();
 
     return (float)distribCf;
 }
 }