diff --git a/src/History.h b/src/History.h
--- a/src/History.h
+++ b/src/History.h
@@ -141,7 +141,7 @@
 private:
     int startOfLine(int lineno);
 
-    HistoryFile _index; // lines Row(int)
+    QVector<int> _index; // lines Row(int)
     HistoryFile _cells; // text  Row(Character)
     HistoryFile _lineflags; // flags Row(unsigned char)
 };
diff --git a/src/History.cpp b/src/History.cpp
--- a/src/History.cpp
+++ b/src/History.cpp
@@ -226,14 +226,15 @@
 
 HistoryScrollFile::HistoryScrollFile(const QString& logFileName)
     : HistoryScroll(new HistoryTypeFile(logFileName))
+    , _index(QVector<int>())
 {
 }
 
 HistoryScrollFile::~HistoryScrollFile() = default;
 
 int HistoryScrollFile::getLines()
 {
-    return _index.len() / sizeof(int);
+    return _index.size();
 }
 
 int HistoryScrollFile::getLineLen(int lineno)
@@ -255,12 +256,7 @@
 {
     if (lineno <= 0) return 0;
     if (lineno <= getLines()) {
-        if (!_index.isMapped())
-            _index.map();
-
-        int res;
-        _index.get((unsigned char*)&res, sizeof(int), (lineno - 1)*sizeof(int));
-        return res;
+        return _index.at(lineno-1);
     }
     return _cells.len();
 }
@@ -277,11 +273,7 @@
 
 void HistoryScrollFile::addLine(bool previousWrapped)
 {
-    if (_index.isMapped())
-        _index.unmap();
-
-    int locn = _cells.len();
-    _index.add((unsigned char*)&locn, sizeof(int));
+    _index.append(_cells.len());
     unsigned char flags = previousWrapped ? 0x01 : 0x00;
     _lineflags.add((unsigned char*)&flags, sizeof(unsigned char));
 }