diff --git a/src/libs/3rdparty/syntax-highlighting/src/lib/state.cpp b/src/libs/3rdparty/syntax-highlighting/src/lib/state.cpp
index 4b4faa956db..dfb4d0c24ad 100644
--- a/src/libs/3rdparty/syntax-highlighting/src/lib/state.cpp
+++ b/src/libs/3rdparty/syntax-highlighting/src/lib/state.cpp
@@ -68,7 +68,7 @@ bool StateData::pop(int popCount)
     // keep the initial context alive in any case
     Q_ASSERT(!isEmpty());
     const bool initialContextSurvived = m_contextStack.size() > popCount;
-    m_contextStack.resize(std::max(1, m_contextStack.size() - popCount));
+    m_contextStack.resize(std::max(1, int(m_contextStack.size()) - popCount));
     return initialContextSurvived;
 }
 
diff --git a/src/libs/languageserverprotocol/servercapabilities.cpp b/src/libs/languageserverprotocol/servercapabilities.cpp
index 5d4574e64bc..268d972d442 100644
--- a/src/libs/languageserverprotocol/servercapabilities.cpp
+++ b/src/libs/languageserverprotocol/servercapabilities.cpp
@@ -256,7 +256,11 @@ bool ServerCapabilities::SemanticHighlightingServerCapabilities::isValid(ErrorHi
 {
     return contains(scopesKey) && value(scopesKey).isArray()
            && Utils::allOf(value(scopesKey).toArray(), [](const QJsonValue &array) {
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
                   return array.isArray() && Utils::allOf(array.toArray(), &QJsonValue::isString);
+#else
+                  return array.isArray() && Utils::allOf(array.toArray(), &QJsonValueRef::isString);
+#endif
               });
 }
 
diff --git a/src/plugins/bookmarks/bookmarkfilter.cpp b/src/plugins/bookmarks/bookmarkfilter.cpp
index 0c74ceafeb9..ecaa90ff6ad 100644
--- a/src/plugins/bookmarks/bookmarkfilter.cpp
+++ b/src/plugins/bookmarks/bookmarkfilter.cpp
@@ -89,18 +89,18 @@ QList<LocatorFilterEntry> BookmarkFilter::matchesFor(QFutureInterface<LocatorFil
             filterEntry.extraInfo = bookmark->fileName().toString();
         int highlightIndex = filterEntry.displayName.indexOf(entry, 0, Qt::CaseInsensitive);
         if (highlightIndex >= 0) {
-            filterEntry.highlightInfo = {highlightIndex, entry.length()};
+            filterEntry.highlightInfo = {highlightIndex, int(entry.length())};
         } else  {
             highlightIndex = filterEntry.extraInfo.indexOf(entry, 0, Qt::CaseInsensitive);
             if (highlightIndex >= 0) {
-                filterEntry.highlightInfo = {highlightIndex, entry.length(),
+                filterEntry.highlightInfo = {highlightIndex, int(entry.length()),
                                              LocatorFilterEntry::HighlightInfo::ExtraInfo};
             } else if (colonIndex >= 0) {
                 const QString fileName = entry.left(colonIndex);
                 const QString lineNumber = entry.mid(colonIndex + 1);
                 highlightIndex = filterEntry.displayName.indexOf(fileName, 0, Qt::CaseInsensitive);
                 if (highlightIndex >= 0) {
-                    filterEntry.highlightInfo = {highlightIndex, fileName.length()};
+                    filterEntry.highlightInfo = {highlightIndex, int(fileName.length())};
                     highlightIndex = filterEntry.displayName.indexOf(
                         lineNumber, highlightIndex, Qt::CaseInsensitive);
                     if (highlightIndex >= 0) {
diff --git a/src/plugins/debugger/cdb/cdbengine.cpp b/src/plugins/debugger/cdb/cdbengine.cpp
index 7dd0d8cc843..a0689e4307f 100644
--- a/src/plugins/debugger/cdb/cdbengine.cpp
+++ b/src/plugins/debugger/cdb/cdbengine.cpp
@@ -2294,7 +2294,7 @@ void CdbEngine::parseOutputLine(QString line)
             if (debug)
                 qDebug("### Completed builtin command '%s' for token=%d, %d lines, pending=%d",
                        qPrintable(command.function), m_currentBuiltinResponseToken,
-                       m_currentBuiltinResponse.count('\n'), int(m_commandForToken.size() - 1));
+                       int(m_currentBuiltinResponse.count('\n')), int(m_commandForToken.size() - 1));
             QTC_ASSERT(token == m_currentBuiltinResponseToken, return);
             showMessage(m_currentBuiltinResponse, LogMisc);
             if (command.callback) {
diff --git a/src/plugins/qmakeprojectmanager/qmakeparsernodes.cpp b/src/plugins/qmakeprojectmanager/qmakeparsernodes.cpp
index e3979bbafb6..15f2465c29c 100644
--- a/src/plugins/qmakeprojectmanager/qmakeparsernodes.cpp
+++ b/src/plugins/qmakeprojectmanager/qmakeparsernodes.cpp
@@ -2028,7 +2028,7 @@ InstallsList QmakeProFile::installsList(const QtSupport::ProFileReader *reader,
         const QStringList &itemPaths = reader->values(pathVar);
         if (itemPaths.count() != 1) {
             qDebug("Invalid RHS: Variable '%s' has %d values.",
-                qPrintable(pathVar), itemPaths.count());
+                qPrintable(pathVar), int(itemPaths.count()));
             if (itemPaths.isEmpty()) {
                 qDebug("%s: Ignoring INSTALLS item '%s', because it has no path.",
                     qPrintable(projectFilePath), qPrintable(item));
diff --git a/src/plugins/vcsbase/vcsbaseeditor.h b/src/plugins/vcsbase/vcsbaseeditor.h
index 72df0289ae0..cd9bafee72f 100644
--- a/src/plugins/vcsbase/vcsbaseeditor.h
+++ b/src/plugins/vcsbase/vcsbaseeditor.h
@@ -30,9 +30,9 @@
 #include <texteditor/texteditor.h>
 
 #include <QSet>
+#include <QTextCodec>
 
 QT_BEGIN_NAMESPACE
-class QTextCodec;
 class QTextCursor;
 QT_END_NAMESPACE