diff --git a/src/buffer/katetextblock.h b/src/buffer/katetextblock.h
--- a/src/buffer/katetextblock.h
+++ b/src/buffer/katetextblock.h
@@ -21,6 +21,8 @@
 #ifndef KATE_TEXTBLOCK_H
 #define KATE_TEXTBLOCK_H
 
+#include <unordered_set>
+
 #include <QVector>
 #include <QSet>
 
@@ -206,7 +208,7 @@
      */
     void removeCursor(Kate::TextCursor *cursor)
     {
-        m_cursors.remove(cursor);
+        m_cursors.erase(cursor);
     }
 
     /**
@@ -246,18 +248,20 @@
 
     /**
      * Lines contained in this buffer. These are shared pointers.
+     * We need no sharing, use STL.
      */
-    QVector<Kate::TextLine> m_lines;
+    std::vector<Kate::TextLine> m_lines;
 
     /**
      * Startline of this block
      */
     int m_startLine;
 
     /**
      * Set of cursors for this block.
+     * We need no sharing, use STL.
      */
-    QSet<TextCursor *> m_cursors;
+    std::unordered_set<TextCursor *> m_cursors;
 
     /**
      * Contains for each line-offset the ranges that were cached into it.
diff --git a/src/buffer/katetextblock.cpp b/src/buffer/katetextblock.cpp
--- a/src/buffer/katetextblock.cpp
+++ b/src/buffer/katetextblock.cpp
@@ -57,19 +57,13 @@
     // right input
     Q_ASSERT(line >= startLine());
 
-    // calc internal line
-    line = line - startLine();
-
-    // in range
-    Q_ASSERT(line < m_lines.size());
-
-    // get text line
-    return m_lines.at(line);
+    // get text line, at will bail out on out-of-range
+    return m_lines.at(line - startLine());
 }
 
 void TextBlock::appendLine(const QString &textOfLine)
 {
-    m_lines.append(TextLine::create(textOfLine));
+    m_lines.push_back(TextLine::create(textOfLine));
 }
 
 void TextBlock::clearLines()
@@ -80,7 +74,7 @@
 void TextBlock::text(QString &text) const
 {
     // combine all lines
-    for (int i = 0; i < m_lines.size(); ++i) {
+    for (size_t i = 0; i < m_lines.size(); ++i) {
         // not first line, insert \n
         if (i > 0 || startLine() > 0) {
             text.append(QLatin1Char('\n'));
@@ -212,7 +206,7 @@
         // move last line of previous block to this one, might result in empty block
         TextLine oldFirst = m_lines.at(0);
         int lastLineOfPreviousBlock = previousBlock->lines() - 1;
-        TextLine newFirst = previousBlock->m_lines.last();
+        TextLine newFirst = previousBlock->m_lines.back();
         m_lines[0] = newFirst;
         previousBlock->m_lines.erase(previousBlock->m_lines.begin() + (previousBlock->lines() - 1));
 
@@ -268,7 +262,7 @@
         }
 
         // move cursors of the moved line from previous block to this block now
-        QSet<TextCursor *> newPreviousCursors;
+        std::unordered_set<TextCursor *> newPreviousCursors;
         for (TextCursor *cursor : qAsConst(previousBlock->m_cursors)) {
             if (cursor->lineInBlock() == lastLineOfPreviousBlock) {
                 cursor->m_line = 0;
@@ -522,8 +516,8 @@
 void TextBlock::debugPrint(int blockIndex) const
 {
     // print all blocks
-    for (int i = 0; i < m_lines.size(); ++i)
-        printf("%4d - %4d : %4d : '%s'\n", blockIndex, startLine() + i
+    for (size_t i = 0; i < m_lines.size(); ++i)
+        printf("%4d - %4lld : %4d : '%s'\n", blockIndex, (unsigned long long)startLine() + i
                , m_lines.at(i)->text().size(), qPrintable(m_lines.at(i)->text()));
 }
 
@@ -537,13 +531,13 @@
 
     // move lines
     newBlock->m_lines.reserve(linesOfNewBlock);
-    for (int i = fromLine; i < m_lines.size(); ++i) {
-        newBlock->m_lines.append(m_lines.at(i));
+    for (size_t i = fromLine; i < m_lines.size(); ++i) {
+        newBlock->m_lines.push_back(m_lines.at(i));
     }
     m_lines.resize(fromLine);
 
     // move cursors
-    QSet<TextCursor *> oldBlockSet;
+    std::unordered_set<TextCursor *> oldBlockSet;
     for (TextCursor *cursor : qAsConst(m_cursors)) {
         if (cursor->lineInBlock() >= fromLine) {
             cursor->m_line = cursor->lineInBlock() - fromLine;
@@ -579,8 +573,8 @@
 
     // move lines
     targetBlock->m_lines.reserve(targetBlock->lines() + lines());
-    for (int i = 0; i < m_lines.size(); ++i) {
-        targetBlock->m_lines.append(m_lines.at(i));
+    for (size_t i = 0; i < m_lines.size(); ++i) {
+        targetBlock->m_lines.push_back(m_lines.at(i));
     }
     m_lines.clear();
 
@@ -596,7 +590,7 @@
 void TextBlock::deleteBlockContent()
 {
     // kill cursors, if not belonging to a range
-    QSet<TextCursor *> copy = m_cursors;
+    std::unordered_set<TextCursor *> copy = m_cursors;
     for (TextCursor *cursor : qAsConst(copy)) {
         if (!cursor->kateRange()) {
             delete cursor;
@@ -610,14 +604,20 @@
 void TextBlock::clearBlockContent(TextBlock *targetBlock)
 {
     // move cursors, if not belonging to a range
-    QSet<TextCursor *> copy = m_cursors;
-    for (TextCursor *cursor : qAsConst(copy)) {
+    // we can do in-place editing of the current set of cursors
+    for (auto it = m_cursors.begin(); it != m_cursors.end();) {
+        auto cursor = *it;
         if (!cursor->kateRange()) {
             cursor->m_column = 0;
             cursor->m_line = 0;
             cursor->m_block = targetBlock;
             targetBlock->m_cursors.insert(cursor);
-            m_cursors.remove(cursor);
+
+            // remove it and advance to next element
+            it = m_cursors.erase(it);
+        } else {
+            // keep this cursor
+            ++it;
         }
     }
 
@@ -628,8 +628,7 @@
 void TextBlock::markModifiedLinesAsSaved()
 {
     // mark all modified lines as saved
-    for (int i = 0; i < m_lines.size(); ++i) {
-        TextLine textLine = m_lines[i];
+    for (auto &textLine : m_lines) {
         if (textLine->markedAsModified()) {
             textLine->markAsSavedOnDisk(true);
         }