diff --git a/src/dbus/qdbuserror.cpp b/src/dbus/qdbuserror.cpp
index f486c19fdc..ddc2be7c38 100644
--- a/src/dbus/qdbuserror.cpp
+++ b/src/dbus/qdbuserror.cpp
@@ -257,7 +257,9 @@ static inline QDBusError::ErrorType get(const char *name)
 QDBusError::QDBusError()
     : code(NoError)
 {
-
+    // ### This class has an implicit (therefore inline) destructor
+    // so the following field cannot be used.
+    Q_UNUSED(unused);
 }
 
 #ifndef QT_BOOTSTRAPPED
diff --git a/src/xml/sax/qxml.cpp b/src/xml/sax/qxml.cpp
index 47e137976b..0e20041a62 100644
--- a/src/xml/sax/qxml.cpp
+++ b/src/xml/sax/qxml.cpp
@@ -985,12 +985,22 @@ void QXmlNamespaceSupport::reset()
 
     Constructs an empty attribute list.
 */
+QXmlAttributes::QXmlAttributes()
+{
+    // ### In Qt 5.0, this function was inlined and d was not initialized
+    // The member cannot be used until Qt 6.0
+    Q_UNUSED(d);
+}
 
 /*!
     \fn QXmlAttributes::~QXmlAttributes()
 
     Destroys the attributes object.
 */
+QXmlAttributes::~QXmlAttributes()
+{
+}
+
 
 /*!
     Looks up the index of an attribute by the qualified name \a qName.
@@ -2400,11 +2410,21 @@ events are reported.
 
     Constructs a handler for use with subclasses of QXmlReader.
 */
+QXmlDefaultHandler::QXmlDefaultHandler()
+{
+    // ### In Qt 5.0, this function was inlined and d was not initialized
+    // The member cannot be used until Qt 6.0
+    Q_UNUSED(d);
+}
+
 /*!
     \fn QXmlDefaultHandler::~QXmlDefaultHandler()
 
     Destroys the handler.
 */
+QXmlDefaultHandler::~QXmlDefaultHandler()
+{
+}
 
 /*!
     \reimp
diff --git a/src/xml/sax/qxml.h b/src/xml/sax/qxml.h
index 4ce2c26b05..743f8702af 100644
--- a/src/xml/sax/qxml.h
+++ b/src/xml/sax/qxml.h
@@ -117,8 +117,8 @@ private:
 class Q_XML_EXPORT QXmlAttributes
 {
 public:
-    QXmlAttributes() {}
-    virtual ~QXmlAttributes() {}
+    QXmlAttributes();
+    virtual ~QXmlAttributes();
 
     int index(const QString& qName) const;
     int index(QLatin1String qName) const;
@@ -365,8 +365,8 @@ public:
 class Q_XML_EXPORT QXmlDefaultHandler : public QXmlContentHandler, public QXmlErrorHandler, public QXmlDTDHandler, public QXmlEntityResolver, public QXmlLexicalHandler, public QXmlDeclHandler
 {
 public:
-    QXmlDefaultHandler() { }
-    virtual ~QXmlDefaultHandler() { }
+    QXmlDefaultHandler();
+    virtual ~QXmlDefaultHandler();
 
     void setDocumentLocator(QXmlLocator* locator);
     bool startDocument();