diff --git a/harbour/ChangeLog b/harbour/ChangeLog
index df968b60c3..25b126051e 100644
--- a/harbour/ChangeLog
+++ b/harbour/ChangeLog
@@ -16,6 +16,15 @@
    The license applies to all entries newer than 2009-04-28.
 */
 
+2012-01-03 15:40 UTC+0100 Przemyslaw Czerpak (druzus/at/poczta.onet.pl)
+  * harbour/src/rtl/filebuf.c
+    ! fixed next three integer overflows exploited by HB64 locking mode.
+      BTW probably I'll move the lock range to not operate on last positive
+      offset because such overflow problems can be also exploited in low
+      level OS or network transport layer code - it happened in the past.
+      I'll do that when we confirm that current Harbour implementation
+      is correct.
+
 2012-01-03 10:39 UTC+0100 Przemyslaw Czerpak (druzus/at/poczta.onet.pl)
   * harbour/src/rtl/filebuf.c
     ! fixed integer overflow in code scanning the lock pool.
diff --git a/harbour/src/rtl/filebuf.c b/harbour/src/rtl/filebuf.c
index 614f519650..d46ddd4813 100644
--- a/harbour/src/rtl/filebuf.c
+++ b/harbour/src/rtl/filebuf.c
@@ -233,7 +233,7 @@ static HB_BOOL hb_fileSetLock( PHB_FILE pFile, HB_BOOL * pfLockFS,
    if( uiPos < pFile->uiLocks )
    {
       PHB_FLOCK pLock = &pFile->pLocks[ uiPos ];
-      if( nStart + nLen > pLock->start )
+      if( nStart + nLen - 1 >= pLock->start )
          return HB_FALSE;
       if( nStart + nLen == pLock->start )
          fRJoin = HB_TRUE;
@@ -278,7 +278,7 @@ static HB_BOOL hb_fileUnlock( PHB_FILE pFile, HB_BOOL * pfLockFS,
    {
       PHB_FLOCK pLock = &pFile->pLocks[ uiPos ];
       if( nStart >= pLock->start &&
-          nStart + nLen <= pLock->start + pLock->len )
+          nStart + nLen - 1 <= pLock->start + pLock->len - 1 )
       {
          if( pfLockFS && pFile->shared )
             * pfLockFS = HB_TRUE;
@@ -316,7 +316,7 @@ static HB_BOOL hb_fileTestLock( PHB_FILE pFile,
    if( uiPos < pFile->uiLocks )
    {
       PHB_FLOCK pLock = &pFile->pLocks[ uiPos ];
-      if( nStart + nLen > pLock->start )
+      if( nStart + nLen - 1 >= pLock->start )
          return HB_TRUE;
    }