diff --git a/src/gui/accessible/qaccessible2.h b/src/gui/accessible/qaccessible2.h
index 61e46ebf04..708910b8df 100644
--- a/src/gui/accessible/qaccessible2.h
+++ b/src/gui/accessible/qaccessible2.h
@@ -115,7 +115,7 @@ public:
 class Q_GUI_EXPORT QAccessibleSimpleEditableTextInterface: public QAccessibleEditableTextInterface
 {
 public:
-    QAccessibleSimpleEditableTextInterface(QAccessibleInterface *accessibleInterface);  //###
+    explicit QAccessibleSimpleEditableTextInterface(QAccessibleInterface *accessibleInterface);  //###
 
     void copyText(int startOffset, int endOffset) const;
     void deleteText(int startOffset, int endOffset);
diff --git a/src/gui/image/qmovie.h b/src/gui/image/qmovie.h
index 9d4cb87b15..e11dea6ad3 100644
--- a/src/gui/image/qmovie.h
+++ b/src/gui/image/qmovie.h
@@ -83,7 +83,7 @@ public:
         CacheAll
     };
 
-    QMovie(QObject *parent = 0);
+    explicit QMovie(QObject *parent = 0);
     explicit QMovie(QIODevice *device, const QByteArray &format = QByteArray(), QObject *parent = 0);
     explicit QMovie(const QString &fileName, const QByteArray &format = QByteArray(), QObject *parent = 0);
     ~QMovie();
diff --git a/src/gui/image/qpixmap.h b/src/gui/image/qpixmap.h
index 3d78a43917..0b21be5c8e 100644
--- a/src/gui/image/qpixmap.h
+++ b/src/gui/image/qpixmap.h
@@ -67,10 +67,10 @@ public:
     QPixmap();
     explicit QPixmap(QPlatformPixmap *data);
     QPixmap(int w, int h);
-    QPixmap(const QSize &);
+    explicit QPixmap(const QSize &);
     QPixmap(const QString& fileName, const char *format = 0, Qt::ImageConversionFlags flags = Qt::AutoColor);
 #ifndef QT_NO_IMAGEFORMAT_XPM
-    QPixmap(const char * const xpm[]);
+    explicit QPixmap(const char * const xpm[]);
 #endif
     QPixmap(const QPixmap &);
     ~QPixmap();
diff --git a/src/gui/kernel/qclipboard.h b/src/gui/kernel/qclipboard.h
index 5a251dd0ef..5c88764d88 100644
--- a/src/gui/kernel/qclipboard.h
+++ b/src/gui/kernel/qclipboard.h
@@ -59,7 +59,7 @@ class Q_GUI_EXPORT QClipboard : public QObject
 {
     Q_OBJECT
 private:
-    QClipboard(QObject *parent);
+    explicit QClipboard(QObject *parent);
     ~QClipboard();
 
 public:
diff --git a/src/gui/kernel/qopenglcontext.h b/src/gui/kernel/qopenglcontext.h
index 52f94a8a10..5e1cd17635 100644
--- a/src/gui/kernel/qopenglcontext.h
+++ b/src/gui/kernel/qopenglcontext.h
@@ -94,7 +94,7 @@ class Q_GUI_EXPORT QOpenGLContext : public QObject
     Q_OBJECT
     Q_DECLARE_PRIVATE(QOpenGLContext)
 public:
-    QOpenGLContext(QObject *parent = 0);
+    explicit QOpenGLContext(QObject *parent = 0);
     ~QOpenGLContext();
 
     void setFormat(const QSurfaceFormat &format);
diff --git a/src/gui/kernel/qplatformsharedgraphicscache_qpa.h b/src/gui/kernel/qplatformsharedgraphicscache_qpa.h
index d59cd7c3c8..f8ee201d85 100644
--- a/src/gui/kernel/qplatformsharedgraphicscache_qpa.h
+++ b/src/gui/kernel/qplatformsharedgraphicscache_qpa.h
@@ -65,7 +65,7 @@ public:
         OpenGLTexture
     };
 
-    QPlatformSharedGraphicsCache(QObject *parent = 0) : QObject(parent) {}
+    explicit QPlatformSharedGraphicsCache(QObject *parent = 0) : QObject(parent) {}
 
     Q_INVOKABLE virtual void ensureCacheInitialized(const QByteArray &cacheId, BufferType bufferType,
                                                     PixelFormat pixelFormat) = 0;
diff --git a/src/gui/kernel/qplatformsurface_qpa.h b/src/gui/kernel/qplatformsurface_qpa.h
index af23ad3a85..646c3b72ce 100644
--- a/src/gui/kernel/qplatformsurface_qpa.h
+++ b/src/gui/kernel/qplatformsurface_qpa.h
@@ -59,7 +59,7 @@ public:
     QSurface::SurfaceClass surfaceClass() const;
 
 private:
-    QPlatformSurface(QSurface::SurfaceClass type);
+    explicit QPlatformSurface(QSurface::SurfaceClass type);
 
     QSurface::SurfaceClass m_type;
 
diff --git a/src/gui/kernel/qplatformwindow_qpa.h b/src/gui/kernel/qplatformwindow_qpa.h
index 170f62162f..a72de7b547 100644
--- a/src/gui/kernel/qplatformwindow_qpa.h
+++ b/src/gui/kernel/qplatformwindow_qpa.h
@@ -63,7 +63,7 @@ class Q_GUI_EXPORT QPlatformWindow : public QPlatformSurface
 {
     Q_DECLARE_PRIVATE(QPlatformWindow)
 public:
-    QPlatformWindow(QWindow *window);
+    explicit QPlatformWindow(QWindow *window);
     virtual ~QPlatformWindow();
 
     QWindow *window() const;
diff --git a/src/gui/kernel/qscreen.h b/src/gui/kernel/qscreen.h
index 111e10d340..3bd24db3ce 100644
--- a/src/gui/kernel/qscreen.h
+++ b/src/gui/kernel/qscreen.h
@@ -142,7 +142,7 @@ Q_SIGNALS:
     void orientationChanged(Qt::ScreenOrientation orientation);
 
 private:
-    QScreen(QPlatformScreen *screen);
+    explicit QScreen(QPlatformScreen *screen);
 
     Q_DISABLE_COPY(QScreen)
     friend class QGuiApplicationPrivate;
diff --git a/src/gui/kernel/qsurface.h b/src/gui/kernel/qsurface.h
index a8900fde33..befb771129 100644
--- a/src/gui/kernel/qsurface.h
+++ b/src/gui/kernel/qsurface.h
@@ -80,7 +80,7 @@ public:
     virtual QSize size() const = 0;
 
 protected:
-    QSurface(SurfaceClass type);
+    explicit QSurface(SurfaceClass type);
 
     SurfaceClass m_type;
 
diff --git a/src/gui/kernel/qsurfaceformat.h b/src/gui/kernel/qsurfaceformat.h
index 6daa08095e..a4224bbedd 100644
--- a/src/gui/kernel/qsurfaceformat.h
+++ b/src/gui/kernel/qsurfaceformat.h
@@ -75,7 +75,7 @@ public:
     };
 
     QSurfaceFormat();
-    QSurfaceFormat(FormatOptions options);
+    /*implicit*/ QSurfaceFormat(FormatOptions options);
     QSurfaceFormat(const QSurfaceFormat &other);
     QSurfaceFormat &operator=(const QSurfaceFormat &other);
     ~QSurfaceFormat();
diff --git a/src/gui/kernel/qwindow.h b/src/gui/kernel/qwindow.h
index 1461f12520..62ddb66a75 100644
--- a/src/gui/kernel/qwindow.h
+++ b/src/gui/kernel/qwindow.h
@@ -94,8 +94,8 @@ class Q_GUI_EXPORT QWindow : public QObject, public QSurface
 
 public:
 
-    QWindow(QScreen *screen = 0);
-    QWindow(QWindow *parent);
+    explicit QWindow(QScreen *screen = 0);
+    explicit QWindow(QWindow *parent);
     virtual ~QWindow();
 
     void setSurfaceType(SurfaceType surfaceType);
diff --git a/src/gui/math3d/qgenericmatrix.h b/src/gui/math3d/qgenericmatrix.h
index 0a2446587a..b987ab2334 100644
--- a/src/gui/math3d/qgenericmatrix.h
+++ b/src/gui/math3d/qgenericmatrix.h
@@ -102,7 +102,7 @@ private:
 #endif
     T m[N][M];    // Column-major order to match OpenGL.
 
-    QGenericMatrix(int) {}       // Construct without initializing identity matrix.
+    explicit QGenericMatrix(int) {}       // Construct without initializing identity matrix.
 
 #if !defined(Q_NO_TEMPLATE_FRIENDS)
     template <int NN, int MM, typename TT>
diff --git a/src/gui/math3d/qmatrix4x4.h b/src/gui/math3d/qmatrix4x4.h
index b80fc86f45..8353adfab1 100644
--- a/src/gui/math3d/qmatrix4x4.h
+++ b/src/gui/math3d/qmatrix4x4.h
@@ -201,7 +201,7 @@ private:
     };
 
     // Construct without initializing identity matrix.
-    QMatrix4x4(int) { }
+    explicit QMatrix4x4(int) { }
 
     QMatrix4x4 orthonormalInverse() const;
 
diff --git a/src/gui/opengl/qopenglframebufferobject.h b/src/gui/opengl/qopenglframebufferobject.h
index 63260f1940..9e69cecc58 100644
--- a/src/gui/opengl/qopenglframebufferobject.h
+++ b/src/gui/opengl/qopenglframebufferobject.h
@@ -67,7 +67,7 @@ public:
         Depth
     };
 
-    QOpenGLFramebufferObject(const QSize &size, GLenum target = GL_TEXTURE_2D);
+    explicit QOpenGLFramebufferObject(const QSize &size, GLenum target = GL_TEXTURE_2D);
     QOpenGLFramebufferObject(int width, int height, GLenum target = GL_TEXTURE_2D);
 #if !defined(QT_OPENGL_ES) || defined(Q_QDOC)
     QOpenGLFramebufferObject(const QSize &size, Attachment attachment,
diff --git a/src/gui/opengl/qopenglfunctions.h b/src/gui/opengl/qopenglfunctions.h
index 4e778dda66..ce36a821b6 100644
--- a/src/gui/opengl/qopenglfunctions.h
+++ b/src/gui/opengl/qopenglfunctions.h
@@ -198,7 +198,7 @@ class Q_GUI_EXPORT QOpenGLFunctions
 {
 public:
     QOpenGLFunctions();
-    QOpenGLFunctions(QOpenGLContext *context);
+    explicit QOpenGLFunctions(QOpenGLContext *context);
     ~QOpenGLFunctions() {}
 
     enum OpenGLFeature
diff --git a/src/gui/opengl/qopenglpaintdevice.h b/src/gui/opengl/qopenglpaintdevice.h
index ce3e7cf278..7d4b901fe7 100644
--- a/src/gui/opengl/qopenglpaintdevice.h
+++ b/src/gui/opengl/qopenglpaintdevice.h
@@ -71,7 +71,7 @@ class Q_GUI_EXPORT QOpenGLPaintDevice : public QPaintDevice
 {
     Q_DECLARE_PRIVATE(QOpenGLPaintDevice)
 public:
-    QOpenGLPaintDevice(const QSize &size);
+    explicit QOpenGLPaintDevice(const QSize &size);
     QOpenGLPaintDevice(int width, int height);
     virtual ~QOpenGLPaintDevice();
 
diff --git a/src/gui/painting/qbackingstore.h b/src/gui/painting/qbackingstore.h
index db6884f58d..ead15e7ea6 100644
--- a/src/gui/painting/qbackingstore.h
+++ b/src/gui/painting/qbackingstore.h
@@ -62,7 +62,7 @@ class QPlatformBackingStore;
 class Q_GUI_EXPORT QBackingStore
 {
 public:
-    QBackingStore(QWindow *window);
+    explicit QBackingStore(QWindow *window);
     ~QBackingStore();
 
     QWindow *window() const;
diff --git a/src/gui/painting/qpdfwriter.h b/src/gui/painting/qpdfwriter.h
index 7b0547ad45..c617521369 100644
--- a/src/gui/painting/qpdfwriter.h
+++ b/src/gui/painting/qpdfwriter.h
@@ -57,8 +57,8 @@ class Q_GUI_EXPORT QPdfWriter : public QObject, public QPagedPaintDevice
 {
     Q_OBJECT
 public:
-    QPdfWriter(const QString &filename);
-    QPdfWriter(QIODevice *device);
+    explicit QPdfWriter(const QString &filename);
+    explicit QPdfWriter(QIODevice *device);
     ~QPdfWriter();
 
     QString title() const;
diff --git a/src/gui/painting/qplatformbackingstore_qpa.h b/src/gui/painting/qplatformbackingstore_qpa.h
index 8049c64c25..042913292f 100644
--- a/src/gui/painting/qplatformbackingstore_qpa.h
+++ b/src/gui/painting/qplatformbackingstore_qpa.h
@@ -62,7 +62,7 @@ class QPlatformWindow;
 class Q_GUI_EXPORT QPlatformBackingStore
 {
 public:
-    QPlatformBackingStore(QWindow *window);
+    explicit QPlatformBackingStore(QWindow *window);
     virtual ~QPlatformBackingStore();
 
     QWindow *window() const;
diff --git a/src/gui/painting/qpolygon.h b/src/gui/painting/qpolygon.h
index 0a089d3cf3..726ed434ed 100644
--- a/src/gui/painting/qpolygon.h
+++ b/src/gui/painting/qpolygon.h
@@ -61,9 +61,9 @@ class Q_GUI_EXPORT QPolygon : public QVector<QPoint>
 public:
     inline QPolygon() {}
     inline ~QPolygon() {}
-    inline QPolygon(int size);
+    inline explicit QPolygon(int size);
     inline QPolygon(const QPolygon &a) : QVector<QPoint>(a) {}
-    inline QPolygon(const QVector<QPoint> &v) : QVector<QPoint>(v) {}
+    inline /*implicit*/ QPolygon(const QVector<QPoint> &v) : QVector<QPoint>(v) {}
     QPolygon(const QRect &r, bool closed=false);
     QPolygon(int nPoints, const int *points);
     inline void swap(QPolygon &other) { QVector<QPoint>::swap(other); } // prevent QVector<QPoint><->QPolygon swaps
@@ -135,11 +135,11 @@ class Q_GUI_EXPORT QPolygonF : public QVector<QPointF>
 public:
     inline QPolygonF() {}
     inline ~QPolygonF() {}
-    inline QPolygonF(int size);
+    inline explicit QPolygonF(int size);
     inline QPolygonF(const QPolygonF &a) : QVector<QPointF>(a) {}
-    inline QPolygonF(const QVector<QPointF> &v) : QVector<QPointF>(v) {}
+    inline /*implicit*/ QPolygonF(const QVector<QPointF> &v) : QVector<QPointF>(v) {}
     QPolygonF(const QRectF &r);
-    QPolygonF(const QPolygon &a);
+    /*implicit*/ QPolygonF(const QPolygon &a);
     inline void swap(QPolygonF &other) { QVector<QPointF>::swap(other); } // prevent QVector<QPointF><->QPolygonF swaps
 
     inline void translate(qreal dx, qreal dy);
diff --git a/src/gui/text/qfont.h b/src/gui/text/qfont.h
index 9cc61198a5..cd1e3f0880 100644
--- a/src/gui/text/qfont.h
+++ b/src/gui/text/qfont.h
@@ -272,7 +272,7 @@ public:
     inline void resolve(uint mask) { resolve_mask = mask; }
 
 private:
-    QFont(QFontPrivate *);
+    explicit QFont(QFontPrivate *);
 
     void detach();
 
diff --git a/src/gui/text/qfontmetrics.cpp b/src/gui/text/qfontmetrics.cpp
index 7209fbdfc3..fe9e1d16c7 100644
--- a/src/gui/text/qfontmetrics.cpp
+++ b/src/gui/text/qfontmetrics.cpp
@@ -535,7 +535,7 @@ int QFontMetrics::width(const QString &text, int len, int flags) const
         return qRound(width);
     }
 
-    QStackTextEngine layout(text, d.data());
+    QStackTextEngine layout(text, QFont(d.data()));
     layout.ignoreBidi = true;
     return qRound(layout.width(0, len));
 }
@@ -611,7 +611,7 @@ int QFontMetrics::charWidth(const QString &text, int pos) const
         int from = qMax(0, pos - 8);
         int to = qMin(text.length(), pos + 8);
         QString cstr = QString::fromRawData(text.unicode() + from, to - from);
-        QStackTextEngine layout(cstr, d.data());
+        QStackTextEngine layout(cstr, QFont(d.data()));
         layout.ignoreBidi = true;
         layout.itemize();
         width = qRound(layout.width(pos-from, 1));
@@ -660,7 +660,7 @@ QRect QFontMetrics::boundingRect(const QString &text) const
     if (text.length() == 0)
         return QRect();
 
-    QStackTextEngine layout(text, d.data());
+    QStackTextEngine layout(text, QFont(d.data()));
     layout.ignoreBidi = true;
     layout.itemize();
     glyph_metrics_t gm = layout.boundingBox(0, text.length());
@@ -830,7 +830,7 @@ QRect QFontMetrics::tightBoundingRect(const QString &text) const
     if (text.length() == 0)
         return QRect();
 
-    QStackTextEngine layout(text, d.data());
+    QStackTextEngine layout(text, QFont(d.data()));
     layout.ignoreBidi = true;
     layout.itemize();
     glyph_metrics_t gm = layout.tightBoundingBox(0, text.length());
@@ -1364,7 +1364,7 @@ qreal QFontMetricsF::width(const QString &text) const
     int pos = text.indexOf(QLatin1Char('\x9c'));
     int len = (pos != -1) ? pos : text.length();
 
-    QStackTextEngine layout(text, d.data());
+    QStackTextEngine layout(text, QFont(d.data()));
     layout.ignoreBidi = true;
     layout.itemize();
     return layout.width(0, len).toReal();
@@ -1441,7 +1441,7 @@ QRectF QFontMetricsF::boundingRect(const QString &text) const
     if (len == 0)
         return QRectF();
 
-    QStackTextEngine layout(text, d.data());
+    QStackTextEngine layout(text, QFont(d.data()));
     layout.ignoreBidi = true;
     layout.itemize();
     glyph_metrics_t gm = layout.boundingBox(0, len);
@@ -1614,7 +1614,7 @@ QRectF QFontMetricsF::tightBoundingRect(const QString &text) const
     if (text.length() == 0)
         return QRect();
 
-    QStackTextEngine layout(text, d.data());
+    QStackTextEngine layout(text, QFont(d.data()));
     layout.ignoreBidi = true;
     layout.itemize();
     glyph_metrics_t gm = layout.tightBoundingBox(0, text.length());
diff --git a/src/gui/text/qsyntaxhighlighter.h b/src/gui/text/qsyntaxhighlighter.h
index 244f40b7ed..7107238a95 100644
--- a/src/gui/text/qsyntaxhighlighter.h
+++ b/src/gui/text/qsyntaxhighlighter.h
@@ -66,8 +66,8 @@ class Q_GUI_EXPORT QSyntaxHighlighter : public QObject
     Q_OBJECT
     Q_DECLARE_PRIVATE(QSyntaxHighlighter)
 public:
-    QSyntaxHighlighter(QObject *parent);
-    QSyntaxHighlighter(QTextDocument *parent);
+    explicit QSyntaxHighlighter(QObject *parent);
+    explicit QSyntaxHighlighter(QTextDocument *parent);
     virtual ~QSyntaxHighlighter();
 
     void setDocument(QTextDocument *doc);
diff --git a/src/gui/text/qtextdocumentwriter.h b/src/gui/text/qtextdocumentwriter.h
index c0dea06f8f..b7743b1ff7 100644
--- a/src/gui/text/qtextdocumentwriter.h
+++ b/src/gui/text/qtextdocumentwriter.h
@@ -59,7 +59,7 @@ class Q_GUI_EXPORT QTextDocumentWriter
 public:
     QTextDocumentWriter();
     QTextDocumentWriter(QIODevice *device, const QByteArray &format);
-    QTextDocumentWriter(const QString &fileName, const QByteArray &format = QByteArray());
+    explicit QTextDocumentWriter(const QString &fileName, const QByteArray &format = QByteArray());
     ~QTextDocumentWriter();
 
     void setFormat (const QByteArray &format);
diff --git a/src/gui/text/qtextlayout.cpp b/src/gui/text/qtextlayout.cpp
index 56098b0bdb..95b8f48ec5 100644
--- a/src/gui/text/qtextlayout.cpp
+++ b/src/gui/text/qtextlayout.cpp
@@ -340,7 +340,7 @@ QTextLayout::QTextLayout(const QString& text, const QFont &font, QPaintDevice *p
     QFont f(font);
     if (paintdevice)
         f = QFont(font, paintdevice);
-    d = new QTextEngine((text.isNull() ? (const QString&)QString::fromLatin1("") : text), f.d.data());
+    d = new QTextEngine((text.isNull() ? (const QString&)QString::fromLatin1("") : text), f);
 }
 
 /*!
diff --git a/src/gui/text/qtextoption.h b/src/gui/text/qtextoption.h
index a0a4c76282..96a0cdda9b 100644
--- a/src/gui/text/qtextoption.h
+++ b/src/gui/text/qtextoption.h
@@ -86,7 +86,7 @@ public:
     };
 
     QTextOption();
-    QTextOption(Qt::Alignment alignment);
+    /*implicit*/ QTextOption(Qt::Alignment alignment);
     ~QTextOption();
 
     QTextOption(const QTextOption &o);
diff --git a/src/gui/util/qvalidator.h b/src/gui/util/qvalidator.h
index f3191d2b1b..7aa8ad4091 100644
--- a/src/gui/util/qvalidator.h
+++ b/src/gui/util/qvalidator.h
@@ -176,7 +176,7 @@ class Q_GUI_EXPORT QRegExpValidator : public QValidator
 
 public:
     explicit QRegExpValidator(QObject *parent = 0);
-    QRegExpValidator(const QRegExp& rx, QObject *parent = 0);
+    explicit QRegExpValidator(const QRegExp& rx, QObject *parent = 0);
     ~QRegExpValidator();
 
     virtual QValidator::State validate(QString& input, int& pos) const;