diff --git a/src/widgets/accessmanager.h b/src/widgets/accessmanager.h
--- a/src/widgets/accessmanager.h
+++ b/src/widgets/accessmanager.h
@@ -91,7 +91,7 @@
     /**
      * Constructor
      */
-    AccessManager(QObject *parent);
+    explicit AccessManager(QObject *parent);
 
     /**
      * Destructor
diff --git a/src/widgets/dndpopupmenuplugin.h b/src/widgets/dndpopupmenuplugin.h
--- a/src/widgets/dndpopupmenuplugin.h
+++ b/src/widgets/dndpopupmenuplugin.h
@@ -51,7 +51,7 @@
     /**
      * Constructor.
      */
-    DndPopupMenuPlugin(QObject* parent);
+    explicit DndPopupMenuPlugin(QObject* parent);
     virtual ~DndPopupMenuPlugin();
 
     /**
diff --git a/src/widgets/kabstractfileitemactionplugin.h b/src/widgets/kabstractfileitemactionplugin.h
--- a/src/widgets/kabstractfileitemactionplugin.h
+++ b/src/widgets/kabstractfileitemactionplugin.h
@@ -90,7 +90,7 @@
     Q_OBJECT
 
 public:
-    KAbstractFileItemActionPlugin(QObject *parent);
+    explicit KAbstractFileItemActionPlugin(QObject *parent);
 
     virtual ~KAbstractFileItemActionPlugin();
 
diff --git a/src/widgets/kdirlister.h b/src/widgets/kdirlister.h
--- a/src/widgets/kdirlister.h
+++ b/src/widgets/kdirlister.h
@@ -40,7 +40,7 @@
     /**
      * Create a directory lister.
      */
-    KDirLister(QObject *parent = nullptr);
+    explicit KDirLister(QObject *parent = nullptr);
 
     /**
      * Destroy the directory lister.
diff --git a/src/widgets/kfileitemactions.h b/src/widgets/kfileitemactions.h
--- a/src/widgets/kfileitemactions.h
+++ b/src/widgets/kfileitemactions.h
@@ -63,7 +63,7 @@
      * Note that this instance must stay alive for at least as long as the popupmenu;
      * it has the slots for the actions created by addOpenWithActionsTo/addServiceActionsTo.
      */
-    KFileItemActions(QObject *parent = nullptr);
+    explicit KFileItemActions(QObject *parent = nullptr);
 
     /**
      * Destructor
diff --git a/src/widgets/kopenwithdialog.h b/src/widgets/kopenwithdialog.h
--- a/src/widgets/kopenwithdialog.h
+++ b/src/widgets/kopenwithdialog.h
@@ -86,7 +86,7 @@
      *
      * @param parent parent widget
      */
-    KOpenWithDialog(QWidget *parent = nullptr);
+    explicit KOpenWithDialog(QWidget *parent = nullptr);
 
     /**
      * Destructor
diff --git a/src/widgets/kpropertiesdialog.h b/src/widgets/kpropertiesdialog.h
--- a/src/widgets/kpropertiesdialog.h
+++ b/src/widgets/kpropertiesdialog.h
@@ -415,7 +415,7 @@
      * To insert tabs into the properties dialog, use the add methods provided by
      * KPageDialog (the properties dialog is a KPageDialog).
      */
-    KPropertiesDialogPlugin(KPropertiesDialog *_props);
+    explicit KPropertiesDialogPlugin(KPropertiesDialog *_props);
     virtual ~KPropertiesDialogPlugin();
 
     /**
diff --git a/src/widgets/kurlcompletion.h b/src/widgets/kurlcompletion.h
--- a/src/widgets/kurlcompletion.h
+++ b/src/widgets/kurlcompletion.h
@@ -64,7 +64,7 @@
      * This overloaded constructor allows you to set the Mode to ExeCompletion
      * or FileCompletion without using setMode. Default is FileCompletion.
      */
-    KUrlCompletion(Mode);
+    explicit KUrlCompletion(Mode);
     /**
      * Destructs the KUrlCompletion object.
      */