diff --git a/mkspecs/features/qt_common.prf b/mkspecs/features/qt_common.prf
index 004b32fd22..843916b3b1 100644
--- a/mkspecs/features/qt_common.prf
+++ b/mkspecs/features/qt_common.prf
@@ -90,14 +90,8 @@ clang {
     greaterThan(QT_GCC_MAJOR_VERSION, 5): QMAKE_CXXFLAGS_WARN_ON += -Wshift-overflow=2 -Wduplicated-cond
     # GCC 7 has a lot of false positives relating to this, so disable completely
     greaterThan(QT_GCC_MAJOR_VERSION, 6): QMAKE_CXXFLAGS_WARN_ON += -Wno-stringop-overflow
-    # GCC 9 has a lot of false positives relating to this, so disable completely
-    greaterThan(QT_GCC_MAJOR_VERSION, 8): QMAKE_CXXFLAGS_WARN_ON += -Wno-deprecated-copy
-    # GCC 9 introduced this
-    greaterThan(QT_GCC_MAJOR_VERSION, 8): QMAKE_CXXFLAGS_WARN_ON += -Wno-redundant-move
-    # GCC 9 introduced this
+    # GCC 9 introduced -Wformat-overflow in -Wall, but it is buggy:
     greaterThan(QT_GCC_MAJOR_VERSION, 8): QMAKE_CXXFLAGS_WARN_ON += -Wno-format-overflow
-    # GCC 9 introduced this
-    greaterThan(QT_GCC_MAJOR_VERSION, 8): QMAKE_CXXFLAGS_WARN_ON += -Wno-init-list-lifetime
 }
 
 warnings_are_errors:warning_clean {
@@ -137,14 +131,13 @@ warnings_are_errors:warning_clean {
 
             # GCC 7 includes -Wimplicit-fallthrough in -Wextra, but Qt is not yet free of implicit fallthroughs.
             greaterThan(QT_GCC_MAJOR_VERSION, 6): QMAKE_CXXFLAGS_WARN_ON += -Wno-error=implicit-fallthrough
-            # GCC 9 has a lot of false positives relating to this, so disable completely
-            greaterThan(QT_GCC_MAJOR_VERSION, 8): QMAKE_CXXFLAGS_WARN_ON += -Wno-deprecated-copy
+            # GCC 9 introduced -Wdeprecated-copy in -Wextra, but we are not clean for it.
+            greaterThan(QT_GCC_MAJOR_VERSION, 8): QMAKE_CXXFLAGS_WARN_ON += -Wno-error=deprecated-copy
             # GCC 9 introduced this
-            greaterThan(QT_GCC_MAJOR_VERSION, 8): QMAKE_CXXFLAGS_WARN_ON += -Wno-redundant-move
+            greaterThan(QT_GCC_MAJOR_VERSION, 8): QMAKE_CXXFLAGS_WARN_ON += -Wno-error=redundant-move
             # GCC 9 introduced this
-            greaterThan(QT_GCC_MAJOR_VERSION, 8): QMAKE_CXXFLAGS_WARN_ON += -Wno-format-overflow
-            # GCC 9 introduced this
-            greaterThan(QT_GCC_MAJOR_VERSION, 8): QMAKE_CXXFLAGS_WARN_ON += -Wno-init-list-lifetime
+            greaterThan(QT_GCC_MAJOR_VERSION, 8): QMAKE_CXXFLAGS_WARN_ON += -Wno-error=init-list-lifetime
+
             # Work-around for bug https://code.google.com/p/android/issues/detail?id=58135
             android: QMAKE_CXXFLAGS_WARN_ON += -Wno-error=literal-suffix
         }
diff --git a/src/corelib/io/qprocess_p.h b/src/corelib/io/qprocess_p.h
index aa7ecbe91d..eb2d1ed048 100644
--- a/src/corelib/io/qprocess_p.h
+++ b/src/corelib/io/qprocess_p.h
@@ -108,8 +108,7 @@ using QProcEnvKey = QByteArray;
 class QProcEnvValue
 {
 public:
-    QProcEnvValue() {}
-    QProcEnvValue(const QProcEnvValue &other) { *this = other; }
+    QProcEnvValue() = default;
     explicit QProcEnvValue(const QString &value) : stringValue(value) {}
     explicit QProcEnvValue(const QByteArray &value) : byteValue(value) {}
     bool operator==(const QProcEnvValue &other) const
diff --git a/src/corelib/kernel/qvariant.h b/src/corelib/kernel/qvariant.h
index f95502e75f..3cc6d559c1 100644
--- a/src/corelib/kernel/qvariant.h
+++ b/src/corelib/kernel/qvariant.h
@@ -398,10 +398,13 @@ class Q_CORE_EXPORT QVariant
             : type(variantType), is_shared(false), is_null(false)
         {}
 
-        inline Private(const Private &other) Q_DECL_NOTHROW
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
+        Private(const Private &other) Q_DECL_NOTHROW
             : data(other.data), type(other.type),
               is_shared(other.is_shared), is_null(other.is_null)
         {}
+        Private &operator=(const Private &other) Q_DECL_NOTHROW = default;
+#endif
         union Data
         {
             char c;
diff --git a/src/corelib/tools/qbytearraylist.h b/src/corelib/tools/qbytearraylist.h
index d69e8bb54b..1261e1757c 100644
--- a/src/corelib/tools/qbytearraylist.h
+++ b/src/corelib/tools/qbytearraylist.h
@@ -67,7 +67,7 @@ template <> struct QListSpecialMethods<QByteArray>
 {
 #ifndef Q_CLANG_QDOC
 protected:
-    ~QListSpecialMethods() {}
+    ~QListSpecialMethods() = default;
 #endif
 public:
     inline QByteArray join() const
diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index 6643288bd5..e593ba9aa3 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -73,7 +73,7 @@ template <typename T> class QSet;
 template <typename T> struct QListSpecialMethods
 {
 protected:
-    ~QListSpecialMethods() {}
+    ~QListSpecialMethods() = default;
 };
 template <> struct QListSpecialMethods<QByteArray>;
 template <> struct QListSpecialMethods<QString>;
@@ -249,6 +249,8 @@ public:
         // can't remove it in Qt 5, since doing so would make the type trivial,
         // which changes the way it's passed to functions by value.
         inline iterator(const iterator &o) Q_DECL_NOTHROW : i(o.i){}
+        inline iterator &operator=(const iterator &o) Q_DECL_NOTHROW
+        { i = o.i; return *this; }
 #endif
         inline T &operator*() const { return i->t(); }
         inline T *operator->() const { return &i->t(); }
@@ -302,6 +304,8 @@ public:
         // can't remove it in Qt 5, since doing so would make the type trivial,
         // which changes the way it's passed to functions by value.
         inline const_iterator(const const_iterator &o) Q_DECL_NOTHROW : i(o.i) {}
+        inline const_iterator &operator=(const const_iterator &o) Q_DECL_NOTHROW
+        { i = o.i; return *this; }
 #endif
 #ifdef QT_STRICT_ITERATORS
         inline explicit const_iterator(const iterator &o) Q_DECL_NOTHROW : i(o.i) {}
diff --git a/src/corelib/tools/qstringlist.h b/src/corelib/tools/qstringlist.h
index b6c48488df..6b04b7aef1 100644
--- a/src/corelib/tools/qstringlist.h
+++ b/src/corelib/tools/qstringlist.h
@@ -66,7 +66,7 @@ template <> struct QListSpecialMethods<QString>
 {
 #ifndef Q_QDOC
 protected:
-    ~QListSpecialMethods() {}
+    ~QListSpecialMethods() = default;
 #endif
 public:
     inline void sort(Qt::CaseSensitivity cs = Qt::CaseSensitive);
diff --git a/src/gui/painting/qtriangulator_p.h b/src/gui/painting/qtriangulator_p.h
index 8f043fc925..c9ae2571f4 100644
--- a/src/gui/painting/qtriangulator_p.h
+++ b/src/gui/painting/qtriangulator_p.h
@@ -93,6 +93,8 @@ public:
         return indices16.size();
     }
 
+    QVertexIndexVector() = default;
+    QVertexIndexVector(const QVertexIndexVector &other) = default;
     inline QVertexIndexVector &operator = (const QVertexIndexVector &other)
     {
         if (t == UnsignedInt)
diff --git a/src/gui/text/qtextobject.h b/src/gui/text/qtextobject.h
index 067f8473ea..694eb729d5 100644
--- a/src/gui/text/qtextobject.h
+++ b/src/gui/text/qtextobject.h
@@ -263,6 +263,7 @@ public:
         iterator() : p(nullptr), b(0), e(0), n(0) {}
 #if QT_VERSION < QT_VERSION_CHECK(6,0,0)
         iterator(const iterator &o) : p(o.p), b(o.b), e(o.e), n(o.n) {}
+        iterator &operator=(const iterator &o) = default;
 #endif
 
         QTextFragment fragment() const;
diff --git a/src/widgets/styles/qstyleoption.h b/src/widgets/styles/qstyleoption.h
index 8ae07efc81..763575ff5b 100644
--- a/src/widgets/styles/qstyleoption.h
+++ b/src/widgets/styles/qstyleoption.h
@@ -118,6 +118,7 @@ public:
 
     QStyleOptionFocusRect();
     QStyleOptionFocusRect(const QStyleOptionFocusRect &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionFocusRect &operator=(const QStyleOptionFocusRect &other) = default;
 
 protected:
     QStyleOptionFocusRect(int version);
@@ -142,6 +143,7 @@ public:
 
     QStyleOptionFrame();
     QStyleOptionFrame(const QStyleOptionFrame &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionFrame &operator=(const QStyleOptionFrame &other) = default;
 
 protected:
     QStyleOptionFrame(int version);
@@ -171,6 +173,7 @@ public:
     QStyleOptionTabWidgetFrame();
     inline QStyleOptionTabWidgetFrame(const QStyleOptionTabWidgetFrame &other)
         : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionTabWidgetFrame &operator=(const QStyleOptionTabWidgetFrame &other) = default;
 
 protected:
     QStyleOptionTabWidgetFrame(int version);
@@ -194,6 +197,7 @@ public:
 
     QStyleOptionTabBarBase();
     QStyleOptionTabBarBase(const QStyleOptionTabBarBase &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionTabBarBase &operator=(const QStyleOptionTabBarBase &other) = default;
 
 protected:
     QStyleOptionTabBarBase(int version);
@@ -225,6 +229,7 @@ public:
 
     QStyleOptionHeader();
     QStyleOptionHeader(const QStyleOptionHeader &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionHeader &operator=(const QStyleOptionHeader &other) = default;
 
 protected:
     QStyleOptionHeader(int version);
@@ -247,6 +252,7 @@ public:
 
     QStyleOptionButton();
     QStyleOptionButton(const QStyleOptionButton &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionButton &operator=(const QStyleOptionButton &other) = default;
 
 protected:
     QStyleOptionButton(int version);
@@ -284,6 +290,7 @@ public:
 
     QStyleOptionTab();
     QStyleOptionTab(const QStyleOptionTab &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionTab &operator=(const QStyleOptionTab &other) = default;
 
 protected:
     QStyleOptionTab(int version);
@@ -314,6 +321,7 @@ public:
     int midLineWidth;
     QStyleOptionToolBar();
     QStyleOptionToolBar(const QStyleOptionToolBar &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionToolBar &operator=(const QStyleOptionToolBar &other) = default;
 
 protected:
     QStyleOptionToolBar(int version);
@@ -341,6 +349,7 @@ public:
 
     QStyleOptionProgressBar();
     QStyleOptionProgressBar(const QStyleOptionProgressBar &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionProgressBar &operator=(const QStyleOptionProgressBar &other) = default;
 
 protected:
     QStyleOptionProgressBar(int version);
@@ -371,6 +380,7 @@ public:
 
     QStyleOptionMenuItem();
     QStyleOptionMenuItem(const QStyleOptionMenuItem &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionMenuItem &operator=(const QStyleOptionMenuItem &other) = default;
 
 protected:
     QStyleOptionMenuItem(int version);
@@ -390,6 +400,7 @@ public:
 
     QStyleOptionDockWidget();
     QStyleOptionDockWidget(const QStyleOptionDockWidget &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionDockWidget &operator=(const QStyleOptionDockWidget &other) = default;
 
 protected:
     QStyleOptionDockWidget(int version);
@@ -441,6 +452,7 @@ public:
 
     QStyleOptionViewItem();
     QStyleOptionViewItem(const QStyleOptionViewItem &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionViewItem &operator=(const QStyleOptionViewItem &other) = default;
 
 protected:
     QStyleOptionViewItem(int version);
@@ -471,6 +483,7 @@ public:
 
     QStyleOptionToolBox();
     QStyleOptionToolBox(const QStyleOptionToolBox &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionToolBox &operator=(const QStyleOptionToolBox &other) = default;
 
 protected:
     QStyleOptionToolBox(int version);
@@ -490,6 +503,7 @@ public:
 
     QStyleOptionRubberBand();
     QStyleOptionRubberBand(const QStyleOptionRubberBand &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionRubberBand &operator=(const QStyleOptionRubberBand &other) = default;
 
 protected:
     QStyleOptionRubberBand(int version);
@@ -508,6 +522,7 @@ public:
 
     QStyleOptionComplex(int version = QStyleOptionComplex::Version, int type = SO_Complex);
     QStyleOptionComplex(const QStyleOptionComplex &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionComplex &operator=(const QStyleOptionComplex &other) = default;
 };
 
 #if QT_CONFIG(slider)
@@ -532,6 +547,7 @@ public:
 
     QStyleOptionSlider();
     QStyleOptionSlider(const QStyleOptionSlider &other) : QStyleOptionComplex(Version, Type) { *this = other; }
+    QStyleOptionSlider &operator=(const QStyleOptionSlider &other) = default;
 
 protected:
     QStyleOptionSlider(int version);
@@ -551,6 +567,7 @@ public:
 
     QStyleOptionSpinBox();
     QStyleOptionSpinBox(const QStyleOptionSpinBox &other) : QStyleOptionComplex(Version, Type) { *this = other; }
+    QStyleOptionSpinBox &operator=(const QStyleOptionSpinBox &other) = default;
 
 protected:
     QStyleOptionSpinBox(int version);
@@ -578,6 +595,7 @@ public:
 
     QStyleOptionToolButton();
     QStyleOptionToolButton(const QStyleOptionToolButton &other) : QStyleOptionComplex(Version, Type) { *this = other; }
+    QStyleOptionToolButton &operator=(const QStyleOptionToolButton &other) = default;
 
 protected:
     QStyleOptionToolButton(int version);
@@ -600,6 +618,7 @@ public:
 
     QStyleOptionComboBox();
     QStyleOptionComboBox(const QStyleOptionComboBox &other) : QStyleOptionComplex(Version, Type) { *this = other; }
+    QStyleOptionComboBox &operator=(const QStyleOptionComboBox &other) = default;
 
 protected:
     QStyleOptionComboBox(int version);
@@ -618,6 +637,7 @@ public:
 
     QStyleOptionTitleBar();
     QStyleOptionTitleBar(const QStyleOptionTitleBar &other) : QStyleOptionComplex(Version, Type) { *this = other; }
+    QStyleOptionTitleBar &operator=(const QStyleOptionTitleBar &other) = default;
 
 protected:
     QStyleOptionTitleBar(int version);
@@ -638,6 +658,7 @@ public:
 
     QStyleOptionGroupBox();
     QStyleOptionGroupBox(const QStyleOptionGroupBox &other) : QStyleOptionComplex(Version, Type) { *this = other; }
+    QStyleOptionGroupBox &operator=(const QStyleOptionGroupBox &other) = default;
 protected:
     QStyleOptionGroupBox(int version);
 };
@@ -652,6 +673,7 @@ public:
 
     QStyleOptionSizeGrip();
     QStyleOptionSizeGrip(const QStyleOptionSizeGrip &other) : QStyleOptionComplex(Version, Type) { *this = other; }
+    QStyleOptionSizeGrip &operator=(const QStyleOptionSizeGrip &other) = default;
 protected:
     QStyleOptionSizeGrip(int version);
 };
@@ -668,6 +690,7 @@ public:
 
     QStyleOptionGraphicsItem();
     QStyleOptionGraphicsItem(const QStyleOptionGraphicsItem &other) : QStyleOption(Version, Type) { *this = other; }
+    QStyleOptionGraphicsItem &operator=(const QStyleOptionGraphicsItem &other) = default;
     static qreal levelOfDetailFromTransform(const QTransform &worldTransform);
 protected:
     QStyleOptionGraphicsItem(int version);