diff --git a/src/xml/sax/qxml.h b/src/xml/sax/qxml.h
index 86d0956290..038b0c750f 100644
--- a/src/xml/sax/qxml.h
+++ b/src/xml/sax/qxml.h
@@ -158,7 +158,7 @@ class Q_XML_EXPORT QXmlInputSource
 {
 public:
     QXmlInputSource();
-    QXmlInputSource(QIODevice *dev);
+    explicit QXmlInputSource(QIODevice *dev);
     virtual ~QXmlInputSource();
 
     virtual void setData(const QString& dat);