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);
     }
 
     /**
@@ -256,8 +258,9 @@
 
     /**
      * 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
@@ -268,7 +268,7 @@
         }
 
         // 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;
@@ -543,7 +543,7 @@
     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;
@@ -596,7 +596,7 @@
 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 +610,20 @@
 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;
         }
     }