diff --git a/src/libs/utils/namevaluedictionary.h b/src/libs/utils/namevaluedictionary.h
index bbd80b1f99c..8023c97dfd1 100644
--- a/src/libs/utils/namevaluedictionary.h
+++ b/src/libs/utils/namevaluedictionary.h
@@ -36,6 +36,11 @@ class QTCREATOR_UTILS_EXPORT DictKey
 public:
     DictKey(const QString &name, Qt::CaseSensitivity cs) : name(name), caseSensitivity(cs) {}
 
+    friend bool operator==(const DictKey &k1, const DictKey &k2)
+    {
+        return k1.name.compare(k2.name, k1.caseSensitivity) == 0;
+    }
+
     QString name;
     Qt::CaseSensitivity caseSensitivity;
 };
diff --git a/src/libs/utils/namevaluemodel.cpp b/src/libs/utils/namevaluemodel.cpp
index 462cef4e2a7..0283bd9ba78 100644
--- a/src/libs/utils/namevaluemodel.cpp
+++ b/src/libs/utils/namevaluemodel.cpp
@@ -106,8 +106,8 @@ NameValueModel::~NameValueModel() = default;
 
 QString NameValueModel::indexToVariable(const QModelIndex &index) const
 {
-    return d->m_resultNameValueDictionary.key(d->m_resultNameValueDictionary.constBegin()
-                                              + index.row());
+    const auto it = std::next(d->m_resultNameValueDictionary.constBegin(), index.row());
+    return d->m_resultNameValueDictionary.key(it);
 }
 
 void NameValueModel::setBaseNameValueDictionary(const NameValueDictionary &dictionary)
@@ -150,7 +150,8 @@ QVariant NameValueModel::data(const QModelIndex &index, int role) const
     if (!index.isValid())
         return QVariant();
 
-    const auto resultIterator = d->m_resultNameValueDictionary.constBegin() + index.row();
+    const auto resultIterator = std::next(d->m_resultNameValueDictionary.constBegin(), index.row());
+
     switch (role) {
     case Qt::DisplayRole:
     case Qt::EditRole:
diff --git a/src/plugins/coreplugin/find/highlightscrollbarcontroller.cpp b/src/plugins/coreplugin/find/highlightscrollbarcontroller.cpp
index a6edc2a7814..65666b5bccb 100644
--- a/src/plugins/coreplugin/find/highlightscrollbarcontroller.cpp
+++ b/src/plugins/coreplugin/find/highlightscrollbarcontroller.cpp
@@ -267,7 +267,7 @@ static void insertPosition(QMap<int, int> *map, int position)
 
     bool gluedWithPrev = false;
     if (itNext != map->begin()) {
-        auto itPrev = itNext - 1;
+        auto itPrev = std::prev(itNext);
         const int keyStart = itPrev.key();
         const int keyEnd = itPrev.value();
         if (position >= keyStart && position <= keyEnd)
@@ -285,7 +285,7 @@ static void insertPosition(QMap<int, int> *map, int position)
         itNext = map->erase(itNext);
         if (gluedWithPrev) {
             // glue with prev and next
-            auto itPrev = itNext - 1;
+            auto itPrev = std::prev(itNext);
             *itPrev = keyEnd;
         } else {
             // glue with next
diff --git a/src/plugins/diffeditor/sidebysidediffeditorwidget.cpp b/src/plugins/diffeditor/sidebysidediffeditorwidget.cpp
index d9b593befa0..bf411463c00 100644
--- a/src/plugins/diffeditor/sidebysidediffeditorwidget.cpp
+++ b/src/plugins/diffeditor/sidebysidediffeditorwidget.cpp
@@ -328,7 +328,7 @@ int SideDiffEditorWidget::blockNumberForFileIndex(int fileIndex) const
     if (fileIndex < 0 || fileIndex >= m_fileInfo.count())
         return -1;
 
-    return (m_fileInfo.constBegin() + fileIndex).key();
+    return std::next(m_fileInfo.constBegin(), fileIndex).key();
 }
 
 int SideDiffEditorWidget::fileIndexForBlockNumber(int blockNumber) const
diff --git a/src/plugins/diffeditor/unifieddiffeditorwidget.cpp b/src/plugins/diffeditor/unifieddiffeditorwidget.cpp
index c924b668eb6..adc8c108a48 100644
--- a/src/plugins/diffeditor/unifieddiffeditorwidget.cpp
+++ b/src/plugins/diffeditor/unifieddiffeditorwidget.cpp
@@ -587,7 +587,7 @@ int UnifiedDiffEditorWidget::blockNumberForFileIndex(int fileIndex) const
     if (fileIndex < 0 || fileIndex >= m_fileInfo.count())
         return -1;
 
-    return (m_fileInfo.constBegin() + fileIndex).key();
+    return std::next(m_fileInfo.constBegin(), fileIndex).key();
 }
 
 int UnifiedDiffEditorWidget::fileIndexForBlockNumber(int blockNumber) const
diff --git a/src/plugins/fakevim/fakevimplugin.cpp b/src/plugins/fakevim/fakevimplugin.cpp
index 827c5083d3a..b98ba199308 100644
--- a/src/plugins/fakevim/fakevimplugin.cpp
+++ b/src/plugins/fakevim/fakevimplugin.cpp
@@ -697,8 +697,13 @@ void FakeVimExCommandsPage::apply()
         }
         settings->endArray();
         globalCommandMapping.clear();
+#if QT_VERSION >= QT_VERSION_CHECK(5, 15, 0)
+        globalCommandMapping.insert(defaultMap);
+        globalCommandMapping.insert(newMapping);
+#else
         globalCommandMapping.unite(defaultMap);
         globalCommandMapping.unite(newMapping);
+#endif
     }
 }
 
@@ -950,8 +955,13 @@ void FakeVimUserCommandsPage::apply()
         }
         settings->endArray();
         userMap.clear();
+#if QT_VERSION >= QT_VERSION_CHECK(5, 15, 0)
+        userMap.insert(dd->m_defaultUserCommandMap);
+        userMap.insert(current);
+#else
         userMap.unite(dd->m_defaultUserCommandMap);
         userMap.unite(current);
+#endif
     }
 }
 
diff --git a/src/plugins/texteditor/texteditoroverlay.cpp b/src/plugins/texteditor/texteditoroverlay.cpp
index b923b257c3d..863db175c9a 100644
--- a/src/plugins/texteditor/texteditoroverlay.cpp
+++ b/src/plugins/texteditor/texteditoroverlay.cpp
@@ -486,16 +486,16 @@ void TextEditorOverlay::mapEquivalentSelections()
     m_equivalentSelections.clear();
     m_equivalentSelections.resize(m_selections.size());
 
-    QMap<QString, int> all;
+    QMultiMap<QString, int> all;
     for (int i = 0; i < m_selections.size(); ++i)
-        all.insertMulti(selectionText(i).toLower(), i);
+        all.insert(selectionText(i).toLower(), i);
 
     const QList<QString> &uniqueKeys = all.uniqueKeys();
     foreach (const QString &key, uniqueKeys) {
         QList<int> indexes;
         const auto cAll = all;
-        QMap<QString, int>::const_iterator lbit = cAll.lowerBound(key);
-        QMap<QString, int>::const_iterator ubit = cAll.upperBound(key);
+        QMultiMap<QString, int>::const_iterator lbit = cAll.lowerBound(key);
+        QMultiMap<QString, int>::const_iterator ubit = cAll.upperBound(key);
         while (lbit != ubit) {
             indexes.append(lbit.value());
             ++lbit;