diff --git a/gui/aboutdialog.h b/gui/aboutdialog.h
index 7e46839d725..89a36beae79 100644
--- a/gui/aboutdialog.h
+++ b/gui/aboutdialog.h
@@ -40,7 +40,7 @@ class AboutDialog : public QDialog {
 public:
     AboutDialog(const QString &version,
                 const QString &extraVersion,
-                QWidget *parent = nullptr);
+                QWidget *parent);
 
     ~AboutDialog() override;
 
diff --git a/gui/applicationdialog.h b/gui/applicationdialog.h
index 4bc68bf5b13..2c6aca6194c 100644
--- a/gui/applicationdialog.h
+++ b/gui/applicationdialog.h
@@ -50,7 +50,7 @@ class ApplicationDialog : public QDialog {
      */
     ApplicationDialog(const QString &title,
                       Application &app,
-                      QWidget *parent = nullptr);
+                      QWidget *parent);
     ~ApplicationDialog() override;
 
 protected slots:
diff --git a/gui/applicationlist.h b/gui/applicationlist.h
index 537ca51af35..964a9cad4b7 100644
--- a/gui/applicationlist.h
+++ b/gui/applicationlist.h
@@ -36,7 +36,7 @@ class ApplicationList : public QObject {
     Q_OBJECT
 public:
 
-    explicit ApplicationList(QObject *parent = nullptr);
+    explicit ApplicationList(QObject *parent);
     ~ApplicationList() override;
 
     /**
diff --git a/gui/checkstatistics.h b/gui/checkstatistics.h
index 9e064184d99..d6b7f04ac00 100644
--- a/gui/checkstatistics.h
+++ b/gui/checkstatistics.h
@@ -38,7 +38,7 @@
  */
 class CheckStatistics : public QObject {
 public:
-    explicit CheckStatistics(QObject *parent = nullptr);
+    explicit CheckStatistics(QObject *parent);
 
     /**
      * @brief Add new checked item to statistics.
diff --git a/gui/codeeditstyledialog.h b/gui/codeeditstyledialog.h
index 331795d4fbc..861924ffccc 100644
--- a/gui/codeeditstyledialog.h
+++ b/gui/codeeditstyledialog.h
@@ -40,8 +40,8 @@ class QStringList;
 class StyleEditDialog : public QDialog {
     Q_OBJECT
 public:
-    explicit StyleEditDialog(const CodeEditorStyle& newStyle,
-                             QWidget *parent = nullptr);
+    StyleEditDialog(const CodeEditorStyle& newStyle,
+                    QWidget *parent);
 
     CodeEditorStyle getStyle();
 
diff --git a/gui/fileviewdialog.h b/gui/fileviewdialog.h
index 91c455eb869..106a2badea7 100644
--- a/gui/fileviewdialog.h
+++ b/gui/fileviewdialog.h
@@ -44,7 +44,7 @@ class FileViewDialog : public QDialog {
 public:
     FileViewDialog(const QString &file,
                    const QString &title,
-                   QWidget *parent = nullptr);
+                   QWidget *parent);
 
     ~FileViewDialog() override;
 
diff --git a/gui/helpdialog.h b/gui/helpdialog.h
index 075005fd8f2..ea349d01c7a 100644
--- a/gui/helpdialog.h
+++ b/gui/helpdialog.h
@@ -34,7 +34,7 @@ namespace Ui {
 
 class HelpBrowser : public QTextBrowser {
 public:
-    explicit HelpBrowser(QWidget* parent = nullptr) : QTextBrowser(parent) {}
+    explicit HelpBrowser(QWidget* parent) : QTextBrowser(parent) {}
     HelpBrowser(const HelpBrowser&) = delete;
     HelpBrowser(HelpBrowser&&) = delete;
     HelpBrowser& operator=(const HelpBrowser&) = delete;
@@ -49,7 +49,7 @@ class HelpDialog : public QDialog {
     Q_OBJECT
 
 public:
-    explicit HelpDialog(QWidget *parent = nullptr);
+    explicit HelpDialog(QWidget *parent);
     ~HelpDialog() override;
 
 private:
diff --git a/gui/libraryaddfunctiondialog.h b/gui/libraryaddfunctiondialog.h
index d39666defb5..8357245cee1 100644
--- a/gui/libraryaddfunctiondialog.h
+++ b/gui/libraryaddfunctiondialog.h
@@ -36,7 +36,7 @@ class LibraryAddFunctionDialog : public QDialog {
     Q_OBJECT
 
 public:
-    explicit LibraryAddFunctionDialog(QWidget *parent = nullptr);
+    explicit LibraryAddFunctionDialog(QWidget *parent);
     LibraryAddFunctionDialog(const LibraryAddFunctionDialog &) = delete;
     ~LibraryAddFunctionDialog() override;
     LibraryAddFunctionDialog &operator=(const LibraryAddFunctionDialog &) = delete;
diff --git a/gui/librarydialog.cpp b/gui/librarydialog.cpp
index 029f1ce2917..8972846d0b0 100644
--- a/gui/librarydialog.cpp
+++ b/gui/librarydialog.cpp
@@ -185,7 +185,7 @@ void LibraryDialog::saveCfgAs()
 
 void LibraryDialog::addFunction()
 {
-    auto *d = new LibraryAddFunctionDialog;
+    auto *d = new LibraryAddFunctionDialog(nullptr); // TODO: pass parent?
     if (d->exec() == QDialog::Accepted && !d->functionName().isEmpty()) {
 
         CppcheckLibraryData::Function f;
diff --git a/gui/librarydialog.h b/gui/librarydialog.h
index ac27d42756c..d28e193bfd2 100644
--- a/gui/librarydialog.h
+++ b/gui/librarydialog.h
@@ -35,7 +35,7 @@ class LibraryDialog : public QDialog {
     Q_OBJECT
 
 public:
-    explicit LibraryDialog(QWidget *parent = nullptr);
+    explicit LibraryDialog(QWidget *parent);
     LibraryDialog(const LibraryDialog &) = delete;
     ~LibraryDialog() override;
     LibraryDialog &operator=(const LibraryDialog &) = delete;
diff --git a/gui/mainwindow.cpp b/gui/mainwindow.cpp
index eb2905d3475..6c18fd9ed9e 100644
--- a/gui/mainwindow.cpp
+++ b/gui/mainwindow.cpp
@@ -1679,7 +1679,7 @@ void MainWindow::openHelpContents()
 
 void MainWindow::openOnlineHelp()
 {
-    auto *helpDialog = new HelpDialog;
+    auto *helpDialog = new HelpDialog(nullptr); // TODO: pass parent?
     helpDialog->showMaximized();
 }
 
diff --git a/gui/mainwindow.h b/gui/mainwindow.h
index b0721213545..a7338ce8a98 100644
--- a/gui/mainwindow.h
+++ b/gui/mainwindow.h
@@ -72,7 +72,7 @@ class MainWindow : public QMainWindow {
     /**
      * List of checked platforms.
      */
-    Platforms mPlatforms;
+    Platforms mPlatforms{nullptr}; // TODO: pass parent?
 
     /**
      * @brief Analyze given code
diff --git a/gui/newsuppressiondialog.h b/gui/newsuppressiondialog.h
index 436b73abfae..b5159cabcb7 100644
--- a/gui/newsuppressiondialog.h
+++ b/gui/newsuppressiondialog.h
@@ -34,7 +34,7 @@ class NewSuppressionDialog : public QDialog {
     Q_OBJECT
 
 public:
-    explicit NewSuppressionDialog(QWidget *parent = nullptr);
+    explicit NewSuppressionDialog(QWidget *parent);
     NewSuppressionDialog(const NewSuppressionDialog &) = delete;
     ~NewSuppressionDialog() override;
     NewSuppressionDialog &operator=(const NewSuppressionDialog &) = delete;
diff --git a/gui/platforms.h b/gui/platforms.h
index dc941efbc75..d9a9475b554 100644
--- a/gui/platforms.h
+++ b/gui/platforms.h
@@ -46,7 +46,7 @@ class Platforms : public QObject {
     Q_OBJECT
 
 public:
-    explicit Platforms(QObject *parent = nullptr);
+    explicit Platforms(QObject *parent);
     void add(const QString &title, Platform::Type platform);
     int getCount() const;
     void init();
diff --git a/gui/projectfile.h b/gui/projectfile.h
index 328015bb5e2..75e00d0fbc1 100644
--- a/gui/projectfile.h
+++ b/gui/projectfile.h
@@ -47,8 +47,8 @@ class ProjectFile : public QObject {
     Q_OBJECT
 
 public:
-    explicit ProjectFile(QObject *parent = nullptr);
-    explicit ProjectFile(QString filename, QObject *parent = nullptr);
+    explicit ProjectFile(QObject *parent);
+    ProjectFile(QString filename, QObject *parent);
     ~ProjectFile() override {
         if (this == mActiveProject) mActiveProject = nullptr;
     }
diff --git a/gui/projectfiledialog.cpp b/gui/projectfiledialog.cpp
index 47ef75e317f..ebfce3de876 100644
--- a/gui/projectfiledialog.cpp
+++ b/gui/projectfiledialog.cpp
@@ -189,7 +189,7 @@ ProjectFileDialog::ProjectFileDialog(ProjectFile *projectFile, bool premium, QWi
     }
 
     // Platforms..
-    Platforms platforms;
+    Platforms platforms(nullptr); // TODO: pass parent?
     for (const Platform::Type builtinPlatform : builtinPlatforms)
         mUI->mComboBoxPlatform->addItem(platforms.get(builtinPlatform).mTitle);
     QStringList platformFiles;
@@ -869,7 +869,7 @@ void ProjectFileDialog::moveIncludePathDown()
 
 void ProjectFileDialog::addSuppression()
 {
-    NewSuppressionDialog dlg;
+    NewSuppressionDialog dlg(nullptr); // TODO: pass parent?
     if (dlg.exec() == QDialog::Accepted) {
         addSingleSuppression(dlg.getSuppression());
     }
@@ -894,7 +894,7 @@ void ProjectFileDialog::editSuppression(const QModelIndex & /*index*/)
     QListWidgetItem *item = mUI->mListSuppressions->item(row);
     const int suppressionIndex = getSuppressionIndex(item->text());
     if (suppressionIndex >= 0) { // TODO what if suppression is not found?
-        NewSuppressionDialog dlg;
+        NewSuppressionDialog dlg(nullptr); // TODO: pass parent?
         dlg.setSuppression(mSuppressions[suppressionIndex]);
         if (dlg.exec() == QDialog::Accepted) {
             mSuppressions[suppressionIndex] = dlg.getSuppression();
diff --git a/gui/projectfiledialog.h b/gui/projectfiledialog.h
index d9edef245f5..f9aade946bb 100644
--- a/gui/projectfiledialog.h
+++ b/gui/projectfiledialog.h
@@ -45,7 +45,7 @@ class ProjectFile;
 class ProjectFileDialog : public QDialog {
     Q_OBJECT
 public:
-    explicit ProjectFileDialog(ProjectFile *projectFile, bool premium, QWidget *parent = nullptr);
+    ProjectFileDialog(ProjectFile *projectFile, bool premium, QWidget *parent);
     ~ProjectFileDialog() override;
 
 private:
diff --git a/gui/resultstree.h b/gui/resultstree.h
index 213bb7fcdaa..c5fa094d302 100644
--- a/gui/resultstree.h
+++ b/gui/resultstree.h
@@ -52,7 +52,7 @@ enum class Severity;
 class ResultsTree : public QTreeView {
     Q_OBJECT
 public:
-    explicit ResultsTree(QWidget * parent = nullptr);
+    explicit ResultsTree(QWidget * parent);
 
     void initialize(QSettings *settings, ApplicationList *list, ThreadHandler *checkThreadHandler);
 
diff --git a/gui/resultsview.h b/gui/resultsview.h
index 6a9743b2889..592e7112532 100644
--- a/gui/resultsview.h
+++ b/gui/resultsview.h
@@ -52,7 +52,7 @@ class ResultsView : public QWidget {
     Q_OBJECT
 public:
 
-    explicit ResultsView(QWidget * parent = nullptr);
+    explicit ResultsView(QWidget * parent);
     void initialize(QSettings *settings, ApplicationList *list, ThreadHandler *checkThreadHandler);
     ResultsView(const ResultsView &) = delete;
     ~ResultsView() override;
diff --git a/gui/settingsdialog.h b/gui/settingsdialog.h
index 7b1fb694c5f..241ed7e14b2 100644
--- a/gui/settingsdialog.h
+++ b/gui/settingsdialog.h
@@ -48,7 +48,7 @@ class SettingsDialog : public QDialog {
     SettingsDialog(ApplicationList *list,
                    TranslationHandler *translator,
                    bool premium,
-                   QWidget *parent = nullptr);
+                   QWidget *parent);
     SettingsDialog(const SettingsDialog &) = delete;
     ~SettingsDialog() override;
     SettingsDialog &operator=(const SettingsDialog &) = delete;
diff --git a/gui/statsdialog.h b/gui/statsdialog.h
index 62c93fcab58..8b4dd6e3606 100644
--- a/gui/statsdialog.h
+++ b/gui/statsdialog.h
@@ -40,7 +40,7 @@ namespace Ui {
 class StatsDialog : public QDialog {
     Q_OBJECT
 public:
-    explicit StatsDialog(QWidget *parent = nullptr);
+    explicit StatsDialog(QWidget *parent);
     ~StatsDialog() override;
 
     /**
diff --git a/gui/test/projectfile/testprojectfile.cpp b/gui/test/projectfile/testprojectfile.cpp
index 5c69917e8b2..40f1a6c5d15 100644
--- a/gui/test/projectfile/testprojectfile.cpp
+++ b/gui/test/projectfile/testprojectfile.cpp
@@ -49,14 +49,14 @@ bool ImportProject::sourceFileExists(const std::string & /*file*/) {
 void TestProjectFile::loadInexisting() const
 {
     const QString filepath(QString(SRCDIR) + "/../data/projectfiles/foo.cppcheck");
-    ProjectFile pfile(filepath);
+    ProjectFile pfile(filepath, nullptr);
     QCOMPARE(pfile.read(), false);
 }
 
 void TestProjectFile::loadSimple() const
 {
     const QString filepath(QString(SRCDIR) + "/../data/projectfiles/simple.cppcheck");
-    ProjectFile pfile(filepath);
+    ProjectFile pfile(filepath, nullptr);
     QVERIFY(pfile.read());
     QCOMPARE(pfile.getRootPath(), QString("../.."));
     QStringList includes = pfile.getIncludeDirs();
@@ -79,7 +79,7 @@ void TestProjectFile::loadSimple() const
 void TestProjectFile::loadSimpleWithIgnore() const
 {
     const QString filepath(QString(SRCDIR) + "/../data/projectfiles/simple_ignore.cppcheck");
-    ProjectFile pfile(filepath);
+    ProjectFile pfile(filepath, nullptr);
     QVERIFY(pfile.read());
     QCOMPARE(pfile.getRootPath(), QString("../.."));
     QStringList includes = pfile.getIncludeDirs();
@@ -101,7 +101,7 @@ void TestProjectFile::loadSimpleWithIgnore() const
 void TestProjectFile::loadSimpleNoroot() const
 {
     const QString filepath(QString(SRCDIR) + "/../data/projectfiles/simple_noroot.cppcheck");
-    ProjectFile pfile(filepath);
+    ProjectFile pfile(filepath, nullptr);
     QVERIFY(pfile.read());
     QCOMPARE(pfile.getRootPath(), QString());
     QStringList includes = pfile.getIncludeDirs();
@@ -143,7 +143,7 @@ void TestProjectFile::getCheckingSuppressionsRelative() const
 {
     const SuppressionList::Suppression suppression("*", "externals/*");
     const QList<SuppressionList::Suppression> suppressions{suppression};
-    ProjectFile projectFile;
+    ProjectFile projectFile(nullptr);
     projectFile.setFilename("/some/path/123.cppcheck");
     projectFile.setSuppressions(suppressions);
     QCOMPARE(projectFile.getCheckingSuppressions()[0].fileName, "/some/path/externals/*");
@@ -153,7 +153,7 @@ void TestProjectFile::getCheckingSuppressionsAbsolute() const
 {
     const SuppressionList::Suppression suppression("*", "/some/path/1.h");
     const QList<SuppressionList::Suppression> suppressions{suppression};
-    ProjectFile projectFile;
+    ProjectFile projectFile(nullptr);
     projectFile.setFilename("/other/123.cppcheck");
     projectFile.setSuppressions(suppressions);
     QCOMPARE(projectFile.getCheckingSuppressions()[0].fileName, "/some/path/1.h");
@@ -163,7 +163,7 @@ void TestProjectFile::getCheckingSuppressionsStar() const
 {
     const SuppressionList::Suppression suppression("*", "*.cpp");
     const QList<SuppressionList::Suppression> suppressions{suppression};
-    ProjectFile projectFile;
+    ProjectFile projectFile(nullptr);
     projectFile.setFilename("/some/path/123.cppcheck");
     projectFile.setSuppressions(suppressions);
     QCOMPARE(projectFile.getCheckingSuppressions()[0].fileName, "*.cpp");
diff --git a/gui/test/translationhandler/testtranslationhandler.cpp b/gui/test/translationhandler/testtranslationhandler.cpp
index 7abb1c8f7c0..71d3a716fad 100644
--- a/gui/test/translationhandler/testtranslationhandler.cpp
+++ b/gui/test/translationhandler/testtranslationhandler.cpp
@@ -35,7 +35,7 @@ static QStringList getTranslationNames(const TranslationHandler& handler)
 
 void TestTranslationHandler::construct() const
 {
-    TranslationHandler handler;
+    TranslationHandler handler(nullptr);
     QCOMPARE(getTranslationNames(handler).size(), 13);  // 12 translations + english
     QCOMPARE(handler.getCurrentLanguage(), QString("en"));
 }
diff --git a/gui/threadhandler.h b/gui/threadhandler.h
index 5110daaf5a2..dcf668e3642 100644
--- a/gui/threadhandler.h
+++ b/gui/threadhandler.h
@@ -50,7 +50,7 @@ class ErrorItem;
 class ThreadHandler : public QObject {
     Q_OBJECT
 public:
-    explicit ThreadHandler(QObject *parent = nullptr);
+    explicit ThreadHandler(QObject *parent);
     ~ThreadHandler() override;
 
     /**
diff --git a/gui/translationhandler.h b/gui/translationhandler.h
index 12ed2d4a6c0..14a202915cc 100644
--- a/gui/translationhandler.h
+++ b/gui/translationhandler.h
@@ -62,7 +62,7 @@ struct TranslationInfo {
 class TranslationHandler : QObject {
     Q_OBJECT
 public:
-    explicit TranslationHandler(QObject *parent = nullptr);
+    explicit TranslationHandler(QObject *parent);
 
     /**
      * @brief Get a list of available translations.