diff --git a/gtk/deprecated/gtkcombobox.c b/gtk/deprecated/gtkcombobox.c
index 1e76b38f41..2be8d3b784 100644
--- a/gtk/deprecated/gtkcombobox.c
+++ b/gtk/deprecated/gtkcombobox.c
@@ -3033,7 +3033,7 @@ gtk_combo_box_set_child (GtkComboBox *combo_box,
   GtkComboBoxPrivate *priv = gtk_combo_box_get_instance_private (combo_box);
 
   g_return_if_fail (GTK_IS_COMBO_BOX (combo_box));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || gtk_widget_get_parent (child) == NULL);
 
   if (priv->child)
     gtk_combo_box_remove (combo_box, priv->child);
diff --git a/gtk/gtkaspectframe.c b/gtk/gtkaspectframe.c
index 1cc3dba04b..468c123d6f 100644
--- a/gtk/gtkaspectframe.c
+++ b/gtk/gtkaspectframe.c
@@ -640,7 +640,7 @@ gtk_aspect_frame_set_child (GtkAspectFrame  *self,
                             GtkWidget       *child)
 {
   g_return_if_fail (GTK_IS_ASPECT_FRAME (self));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || self->child == child || gtk_widget_get_parent (child) == NULL);
 
   if (self->child == child)
     return;
diff --git a/gtk/gtkbutton.c b/gtk/gtkbutton.c
index d85586c82e..e0038973d3 100644
--- a/gtk/gtkbutton.c
+++ b/gtk/gtkbutton.c
@@ -1034,7 +1034,10 @@ gtk_button_set_child (GtkButton *button,
   GtkButtonPrivate *priv = gtk_button_get_instance_private (button);
 
   g_return_if_fail (GTK_IS_BUTTON (button));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || priv->child == child || gtk_widget_get_parent (child) == NULL);
+
+  if (priv->child == child)
+    return;
 
   g_clear_pointer (&priv->child, gtk_widget_unparent);
 
diff --git a/gtk/gtkcenterbox.c b/gtk/gtkcenterbox.c
index 97bce16698..367c0eab0b 100644
--- a/gtk/gtkcenterbox.c
+++ b/gtk/gtkcenterbox.c
@@ -332,6 +332,12 @@ gtk_center_box_set_start_widget (GtkCenterBox *self,
 {
   GtkLayoutManager *layout_manager;
 
+  g_return_if_fail (GTK_IS_CENTER_BOX (self));
+  g_return_if_fail (child == NULL || self->start_widget == child || gtk_widget_get_parent (child) == NULL);
+
+  if (self->start_widget == child)
+    return;
+
   if (self->start_widget)
     gtk_widget_unparent (self->start_widget);
 
@@ -360,6 +366,12 @@ gtk_center_box_set_center_widget (GtkCenterBox *self,
 {
   GtkLayoutManager *layout_manager;
 
+  g_return_if_fail (GTK_IS_CENTER_BOX (self));
+  g_return_if_fail (child == NULL || self->center_widget == child || gtk_widget_get_parent (child) == NULL);
+
+  if (self->center_widget == child)
+    return;
+
   if (self->center_widget)
     gtk_widget_unparent (self->center_widget);
 
@@ -388,6 +400,12 @@ gtk_center_box_set_end_widget (GtkCenterBox *self,
 {
   GtkLayoutManager *layout_manager;
 
+  g_return_if_fail (GTK_IS_CENTER_BOX (self));
+  g_return_if_fail (child == NULL || self->end_widget == child || gtk_widget_get_parent (child) == NULL);
+
+  if (self->end_widget == child)
+    return;
+
   if (self->end_widget)
     gtk_widget_unparent (self->end_widget);
 
diff --git a/gtk/gtkcheckbutton.c b/gtk/gtkcheckbutton.c
index b639f78faa..aa5af6fcfa 100644
--- a/gtk/gtkcheckbutton.c
+++ b/gtk/gtkcheckbutton.c
@@ -1129,8 +1129,13 @@ void
 gtk_check_button_set_child (GtkCheckButton *button,
                             GtkWidget      *child)
 {
+  GtkCheckButtonPrivate *priv = gtk_check_button_get_instance_private (button);
+
   g_return_if_fail (GTK_IS_CHECK_BUTTON (button));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || priv->child == child || gtk_widget_get_parent (child) == NULL);
+
+  if (priv->child == child)
+    return;
 
   g_object_freeze_notify (G_OBJECT (button));
 
diff --git a/gtk/gtkdragicon.c b/gtk/gtkdragicon.c
index 4035725e25..afcfdf717f 100644
--- a/gtk/gtkdragicon.c
+++ b/gtk/gtkdragicon.c
@@ -480,7 +480,7 @@ gtk_drag_icon_set_child (GtkDragIcon *self,
                          GtkWidget   *child)
 {
   g_return_if_fail (GTK_IS_DRAG_ICON (self));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || gtk_widget_get_parent (child) == NULL);
 
   if (self->child == child)
     return;
diff --git a/gtk/gtkexpander.c b/gtk/gtkexpander.c
index 6b233ebe59..05e20279d5 100644
--- a/gtk/gtkexpander.c
+++ b/gtk/gtkexpander.c
@@ -361,7 +361,7 @@ gtk_expander_class_init (GtkExpanderClass *klass)
                                    PROP_LABEL_WIDGET,
                                    g_param_spec_object ("label-widget", NULL, NULL,
                                                         GTK_TYPE_WIDGET,
-                                                        GTK_PARAM_READWRITE));
+                                                        GTK_PARAM_READWRITE|G_PARAM_EXPLICIT_NOTIFY));
 
   /**
    * GtkExpander:resize-toplevel: (attributes org.gtk.Property.get=gtk_expander_get_resize_toplevel org.gtk.Property.set=gtk_expander_set_resize_toplevel)
@@ -384,7 +384,7 @@ gtk_expander_class_init (GtkExpanderClass *klass)
                                    PROP_CHILD,
                                    g_param_spec_object ("child", NULL, NULL,
                                                         GTK_TYPE_WIDGET,
-                                                        GTK_PARAM_READWRITE));
+                                                        GTK_PARAM_READWRITE|G_PARAM_EXPLICIT_NOTIFY));
 
   /**
    * GtkExpander::activate:
@@ -1091,8 +1091,7 @@ gtk_expander_set_label_widget (GtkExpander *expander,
   GtkWidget *widget;
 
   g_return_if_fail (GTK_IS_EXPANDER (expander));
-  g_return_if_fail (label_widget == NULL || GTK_IS_WIDGET (label_widget));
-  g_return_if_fail (label_widget == NULL || gtk_widget_get_parent (label_widget) == NULL);
+  g_return_if_fail (label_widget == NULL || expander->label_widget == label_widget || gtk_widget_get_parent (label_widget) == NULL);
 
   if (expander->label_widget == label_widget)
     return;
@@ -1185,7 +1184,7 @@ gtk_expander_set_child (GtkExpander *expander,
                         GtkWidget   *child)
 {
   g_return_if_fail (GTK_IS_EXPANDER (expander));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || expander->child == child || gtk_widget_get_parent (child) == NULL);
 
   if (expander->child == child)
     return;
diff --git a/gtk/gtkflowbox.c b/gtk/gtkflowbox.c
index 5b6c8088a1..8650c5a51e 100644
--- a/gtk/gtkflowbox.c
+++ b/gtk/gtkflowbox.c
@@ -597,6 +597,12 @@ gtk_flow_box_child_set_child (GtkFlowBoxChild *self,
 {
   GtkFlowBoxChildPrivate *priv = CHILD_PRIV (self);
 
+  g_return_if_fail (GTK_IS_FLOW_BOX_CHILD (self));
+  g_return_if_fail (child == NULL || priv->child == child || gtk_widget_get_parent (child) == NULL);
+
+  if (priv->child == child)
+    return;
+
   g_clear_pointer (&priv->child, gtk_widget_unparent);
 
   priv->child = child;
diff --git a/gtk/gtkframe.c b/gtk/gtkframe.c
index 9ec452b259..041e05c91c 100644
--- a/gtk/gtkframe.c
+++ b/gtk/gtkframe.c
@@ -188,7 +188,7 @@ gtk_frame_class_init (GtkFrameClass *class)
   frame_props[PROP_LABEL_WIDGET] =
       g_param_spec_object ("label-widget", NULL, NULL,
                            GTK_TYPE_WIDGET,
-                           GTK_PARAM_READWRITE);
+                           GTK_PARAM_READWRITE|G_PARAM_EXPLICIT_NOTIFY);
 
   /**
    * GtkFrame:child: (attributes org.gtk.Property.get=gtk_frame_get_child org.gtk.Property.set=gtk_frame_set_child)
@@ -198,7 +198,7 @@ gtk_frame_class_init (GtkFrameClass *class)
   frame_props[PROP_CHILD] =
       g_param_spec_object ("child", NULL, NULL,
                            GTK_TYPE_WIDGET,
-                           GTK_PARAM_READWRITE);
+                           GTK_PARAM_READWRITE|G_PARAM_EXPLICIT_NOTIFY);
 
   g_object_class_install_properties (gobject_class, LAST_PROP, frame_props);
 
@@ -408,8 +408,7 @@ gtk_frame_set_label_widget (GtkFrame  *frame,
   GtkFramePrivate *priv = gtk_frame_get_instance_private (frame);
 
   g_return_if_fail (GTK_IS_FRAME (frame));
-  g_return_if_fail (label_widget == NULL || GTK_IS_WIDGET (label_widget));
-  g_return_if_fail (label_widget == NULL || gtk_widget_get_parent (label_widget) == NULL);
+  g_return_if_fail (label_widget == NULL || priv->label_widget == label_widget || gtk_widget_get_parent (label_widget) == NULL);
 
   if (priv->label_widget == label_widget)
     return;
@@ -669,7 +668,7 @@ gtk_frame_set_child (GtkFrame  *frame,
   GtkFramePrivate *priv = gtk_frame_get_instance_private (frame);
 
   g_return_if_fail (GTK_IS_FRAME (frame));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || priv->child == child || gtk_widget_get_parent (child) == NULL);
 
   if (priv->child == child)
     return;
diff --git a/gtk/gtkheaderbar.c b/gtk/gtkheaderbar.c
index 671ab59f0b..b0c0963254 100644
--- a/gtk/gtkheaderbar.c
+++ b/gtk/gtkheaderbar.c
@@ -300,8 +300,7 @@ gtk_header_bar_set_title_widget (GtkHeaderBar *bar,
                                  GtkWidget    *title_widget)
 {
   g_return_if_fail (GTK_IS_HEADER_BAR (bar));
-  if (title_widget)
-    g_return_if_fail (GTK_IS_WIDGET (title_widget));
+  g_return_if_fail (title_widget == NULL || bar->title_widget == title_widget || gtk_widget_get_parent (title_widget) == NULL);
 
   /* No need to do anything if the title widget stays the same */
   if (bar->title_widget == title_widget)
@@ -564,7 +563,7 @@ gtk_header_bar_class_init (GtkHeaderBarClass *class)
   header_bar_props[PROP_TITLE_WIDGET] =
       g_param_spec_object ("title-widget", NULL, NULL,
                            GTK_TYPE_WIDGET,
-                           G_PARAM_READWRITE|G_PARAM_STATIC_STRINGS);
+                           G_PARAM_READWRITE|G_PARAM_STATIC_STRINGS|G_PARAM_EXPLICIT_NOTIFY);
 
   /**
    * GtkHeaderBar:show-title-buttons: (attributes org.gtk.Property.get=gtk_header_bar_get_show_title_buttons org.gtk.Property.set=gtk_header_bar_set_show_title_buttons)
diff --git a/gtk/gtklabel.c b/gtk/gtklabel.c
index c5ca7ca095..b8176df846 100644
--- a/gtk/gtklabel.c
+++ b/gtk/gtklabel.c
@@ -2489,7 +2489,7 @@ gtk_label_class_init (GtkLabelClass *class)
   label_props[PROP_MNEMONIC_WIDGET] =
       g_param_spec_object ("mnemonic-widget", NULL, NULL,
                            GTK_TYPE_WIDGET,
-                           GTK_PARAM_READWRITE);
+                           GTK_PARAM_READWRITE|G_PARAM_EXPLICIT_NOTIFY);
 
   /**
    * GtkLabel:ellipsize: (attributes org.gtk.Property.get=gtk_label_get_ellipsize org.gtk.Property.set=gtk_label_set_ellipsize)
@@ -2980,9 +2980,10 @@ gtk_label_set_mnemonic_widget (GtkLabel  *self,
                                GtkWidget *widget)
 {
   g_return_if_fail (GTK_IS_LABEL (self));
+  g_return_if_fail (widget == NULL || GTK_IS_WIDGET (widget));
 
-  if (widget)
-    g_return_if_fail (GTK_IS_WIDGET (widget));
+  if (self->mnemonic_widget == widget)
+    return;
 
   if (self->mnemonic_widget)
     {
diff --git a/gtk/gtklistbox.c b/gtk/gtklistbox.c
index b449051f1b..18dad80889 100644
--- a/gtk/gtklistbox.c
+++ b/gtk/gtklistbox.c
@@ -2956,6 +2956,12 @@ gtk_list_box_row_set_child (GtkListBoxRow *row,
 {
   GtkListBoxRowPrivate *priv = ROW_PRIV (row);
 
+  g_return_if_fail (GTK_IS_LIST_BOX_ROW (row));
+  g_return_if_fail (child == NULL || priv->child == child || gtk_widget_get_parent (child) == NULL);
+
+  if (priv->child == child)
+    return;
+
   g_clear_pointer (&priv->child, gtk_widget_unparent);
 
   priv->child = child;
diff --git a/gtk/gtklistitem.c b/gtk/gtklistitem.c
index 6a357b3dd3..a44752a4da 100644
--- a/gtk/gtklistitem.c
+++ b/gtk/gtklistitem.c
@@ -304,7 +304,7 @@ gtk_list_item_set_child (GtkListItem *self,
                          GtkWidget   *child)
 {
   g_return_if_fail (GTK_IS_LIST_ITEM (self));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || gtk_widget_get_parent (child) == NULL);
 
   if (self->child == child)
     return;
@@ -320,7 +320,7 @@ gtk_list_item_set_child (GtkListItem *self,
   if (self->owner)
     gtk_list_item_widget_set_child (self->owner, child);
 
-  g_object_notify_by_pspec (G_OBJECT (self), properties[PROP_ITEM]);
+  g_object_notify_by_pspec (G_OBJECT (self), properties[PROP_CHILD]);
 }
 
 /**
diff --git a/gtk/gtkmenubutton.c b/gtk/gtkmenubutton.c
index 872be35f1d..ad723aa38b 100644
--- a/gtk/gtkmenubutton.c
+++ b/gtk/gtkmenubutton.c
@@ -1472,7 +1472,10 @@ gtk_menu_button_set_child (GtkMenuButton *menu_button,
   GtkWidget *box, *arrow;
 
   g_return_if_fail (GTK_IS_MENU_BUTTON (menu_button));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || menu_button->child == child || gtk_widget_get_parent (child) == NULL);
+
+  if (menu_button->child == child)
+    return;
 
   g_object_freeze_notify (G_OBJECT (menu_button));
 
@@ -1487,7 +1490,8 @@ gtk_menu_button_set_child (GtkMenuButton *menu_button,
   arrow = gtk_builtin_icon_new ("arrow");
   menu_button->arrow_widget = arrow;
 
-  gtk_box_append (GTK_BOX (box), child);
+  if (child)
+    gtk_box_append (GTK_BOX (box), child);
   gtk_box_append (GTK_BOX (box), arrow);
   gtk_button_set_child (GTK_BUTTON (menu_button->button), box);
 
diff --git a/gtk/gtkoverlay.c b/gtk/gtkoverlay.c
index 4def628f1c..43286c0624 100644
--- a/gtk/gtkoverlay.c
+++ b/gtk/gtkoverlay.c
@@ -570,7 +570,10 @@ gtk_overlay_set_child (GtkOverlay *overlay,
                        GtkWidget  *child)
 {
   g_return_if_fail (GTK_IS_OVERLAY (overlay));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || overlay->child == child || gtk_widget_get_parent (child) == NULL);
+
+  if (overlay->child == child)
+    return;
 
   g_clear_pointer (&overlay->child, gtk_widget_unparent);
 
diff --git a/gtk/gtkpaned.c b/gtk/gtkpaned.c
index 1d5aebe5bf..88aed6675e 100644
--- a/gtk/gtkpaned.c
+++ b/gtk/gtkpaned.c
@@ -1574,11 +1574,14 @@ gtk_paned_new (GtkOrientation orientation)
  * If @child is `NULL`, the existing child will be removed.
  */
 void
-gtk_paned_set_start_child (GtkPaned *paned,
+gtk_paned_set_start_child (GtkPaned  *paned,
                            GtkWidget *child)
 {
   g_return_if_fail (GTK_IS_PANED (paned));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || paned->start_child == child || gtk_widget_get_parent (child) == NULL);
+
+  if (paned->start_child == child)
+    return;
 
   g_clear_pointer (&paned->start_child, gtk_widget_unparent);
 
@@ -1691,11 +1694,14 @@ gtk_paned_get_shrink_start_child (GtkPaned *paned)
  * If @child is `NULL`, the existing child will be removed.
  */
 void
-gtk_paned_set_end_child (GtkPaned *paned,
+gtk_paned_set_end_child (GtkPaned  *paned,
                          GtkWidget *child)
 {
   g_return_if_fail (GTK_IS_PANED (paned));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || paned->end_child == child || gtk_widget_get_parent (child) == NULL);
+
+  if (paned->end_child == child)
+    return;
 
   g_clear_pointer (&paned->end_child, gtk_widget_unparent);
 
diff --git a/gtk/gtkpopover.c b/gtk/gtkpopover.c
index 9aafd1e698..9b62721fac 100644
--- a/gtk/gtkpopover.c
+++ b/gtk/gtkpopover.c
@@ -2009,7 +2009,7 @@ gtk_popover_set_child (GtkPopover *popover,
   GtkPopoverPrivate *priv = gtk_popover_get_instance_private (popover);
 
   g_return_if_fail (GTK_IS_POPOVER (popover));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || priv->child == child || gtk_widget_get_parent (child) == NULL);
 
   if (priv->child == child)
     return;
diff --git a/gtk/gtkrevealer.c b/gtk/gtkrevealer.c
index c0a9938a55..daae048326 100644
--- a/gtk/gtkrevealer.c
+++ b/gtk/gtkrevealer.c
@@ -864,7 +864,10 @@ gtk_revealer_set_child (GtkRevealer *revealer,
                         GtkWidget   *child)
 {
   g_return_if_fail (GTK_IS_REVEALER (revealer));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || revealer->child == child || gtk_widget_get_parent (child) == NULL);
+
+  if (revealer->child == child)
+    return;
 
   g_clear_pointer (&revealer->child, gtk_widget_unparent);
 
diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index be3ab0d4fc..40e4379f69 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -4190,6 +4190,14 @@ gtk_scrolled_window_set_child (GtkScrolledWindow *scrolled_window,
   GtkWidget *scrollable_child;
 
   g_return_if_fail (GTK_IS_SCROLLED_WINDOW (scrolled_window));
+  g_return_if_fail (child == NULL ||
+                    priv->child == child ||
+                    (priv->auto_added_viewport && gtk_viewport_get_child (GTK_VIEWPORT (priv->child)) == child) ||
+                    gtk_widget_get_parent (child) == NULL);
+
+  if (priv->child == child ||
+      (priv->auto_added_viewport && gtk_viewport_get_child (GTK_VIEWPORT (priv->child)) == child))
+    return;
 
   if (priv->child)
     {
diff --git a/gtk/gtksearchbar.c b/gtk/gtksearchbar.c
index bac90c4632..0e2c0be83c 100644
--- a/gtk/gtksearchbar.c
+++ b/gtk/gtksearchbar.c
@@ -675,6 +675,12 @@ void
 gtk_search_bar_set_child (GtkSearchBar *bar,
                           GtkWidget    *child)
 {
+  g_return_if_fail (GTK_IS_SEARCH_BAR (bar));
+  g_return_if_fail (child == NULL || bar->child == child || gtk_widget_get_parent (child) == NULL);
+
+  if (bar->child == child)
+    return;
+
   if (bar->child)
     {
       if (GTK_IS_EDITABLE (bar->child))
diff --git a/gtk/gtktreeexpander.c b/gtk/gtktreeexpander.c
index d4dbfe9596..86230e4028 100644
--- a/gtk/gtktreeexpander.c
+++ b/gtk/gtktreeexpander.c
@@ -782,7 +782,7 @@ gtk_tree_expander_set_child (GtkTreeExpander *self,
                              GtkWidget       *child)
 {
   g_return_if_fail (GTK_IS_TREE_EXPANDER (self));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || self->child == child || gtk_widget_get_parent (child) == NULL);
 
   if (self->child == child)
     return;
diff --git a/gtk/gtkviewport.c b/gtk/gtkviewport.c
index a92d7f62f3..443fec57ee 100644
--- a/gtk/gtkviewport.c
+++ b/gtk/gtkviewport.c
@@ -331,7 +331,7 @@ gtk_viewport_class_init (GtkViewportClass *class)
                                    PROP_CHILD,
                                    g_param_spec_object ("child", NULL, NULL,
                                                         GTK_TYPE_WIDGET,
-                                                        GTK_PARAM_READWRITE));
+                                                        GTK_PARAM_READWRITE|G_PARAM_EXPLICIT_NOTIFY));
 
   gtk_widget_class_set_css_name (widget_class, I_("viewport"));
   gtk_widget_class_set_accessible_role (widget_class, GTK_ACCESSIBLE_ROLE_GROUP);
@@ -686,7 +686,7 @@ gtk_viewport_set_child (GtkViewport *viewport,
                         GtkWidget   *child)
 {
   g_return_if_fail (GTK_IS_VIEWPORT (viewport));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || viewport->child == child || gtk_widget_get_parent (child) == NULL);
 
   if (viewport->child == child)
     return;
diff --git a/gtk/gtkwindow.c b/gtk/gtkwindow.c
index 75b9af1e2b..6f685c355c 100644
--- a/gtk/gtkwindow.c
+++ b/gtk/gtkwindow.c
@@ -6628,7 +6628,10 @@ gtk_window_set_child (GtkWindow *window,
   GtkWindowPrivate *priv = gtk_window_get_instance_private (window);
 
   g_return_if_fail (GTK_IS_WINDOW (window));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || priv->child == child || gtk_widget_get_parent (child) == NULL);
+
+  if (priv->child == child)
+    return;
 
   g_clear_pointer (&priv->child, gtk_widget_unparent);
 
diff --git a/gtk/gtkwindowhandle.c b/gtk/gtkwindowhandle.c
index adfdb8b063..56594d8714 100644
--- a/gtk/gtkwindowhandle.c
+++ b/gtk/gtkwindowhandle.c
@@ -625,7 +625,7 @@ gtk_window_handle_set_child (GtkWindowHandle *self,
                              GtkWidget       *child)
 {
   g_return_if_fail (GTK_IS_WINDOW_HANDLE (self));
-  g_return_if_fail (child == NULL || GTK_IS_WIDGET (child));
+  g_return_if_fail (child == NULL || self->child == child || gtk_widget_get_parent (child) == NULL);
 
   if (self->child == child)
     return;
diff --git a/testsuite/gtk/notify.c b/testsuite/gtk/notify.c
index 9907851c5d..8ee7df88f1 100644
--- a/testsuite/gtk/notify.c
+++ b/testsuite/gtk/notify.c
@@ -86,7 +86,7 @@ check_property (GObject *instance, GParamSpec *pspec)
         first = 1;
       else
         first = 0;
-  
+
       for (i = first; i < class->n_values; i++)
         {
           current_count = data.count + 1;
@@ -161,7 +161,7 @@ check_property (GObject *instance, GParamSpec *pspec)
       assert_notifies (instance, pspec->name, data.count, 1);
 
       g_signal_handler_disconnect (instance, id);
-    } 
+    }
   else if (pspec->value_type == G_TYPE_INT)
     {
       GParamSpecInt *p = G_PARAM_SPEC_INT (pspec);
@@ -283,7 +283,7 @@ check_property (GObject *instance, GParamSpec *pspec)
 
       /* don't check redundant notifications */
       g_object_get (instance, pspec->name, &value, NULL);
-      
+
       if (p->maximum > 100 || p->minimum < -100)
         delta = M_PI;
       else
@@ -323,7 +323,7 @@ check_property (GObject *instance, GParamSpec *pspec)
 
       /* don't check redundant notifications */
       g_object_get (instance, pspec->name, &value, NULL);
-      
+
       new_value = p->minimum;
       for (i = 0; i < 10; i++)
         {
@@ -340,6 +340,29 @@ check_property (GObject *instance, GParamSpec *pspec)
           assert_notifies (instance, pspec->name, data.count, current_count);
         }
 
+      g_signal_handler_disconnect (instance, id);
+    }
+  else if (pspec->value_type == GTK_TYPE_WIDGET)
+    {
+      NotifyData data;
+      gulong id;
+      GtkWidget *value;
+
+      data.name = pspec->name;
+      data.count = 0;
+      id = g_signal_connect (instance, "notify", G_CALLBACK (count_notify), &data);
+
+      value = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 0);
+
+      g_object_set (instance, pspec->name, value, NULL);
+      assert_notifies (instance, pspec->name, data.count, 1);
+
+      g_object_set (instance, pspec->name, value, NULL);
+      assert_notifies (instance, pspec->name, data.count, 1);
+
+      g_object_set (instance, pspec->name, NULL, NULL);
+      assert_notifies (instance, pspec->name, data.count, 2);
+
       g_signal_handler_disconnect (instance, id);
     }
   else
@@ -376,11 +399,6 @@ test_type (gconstpointer data)
   if (g_str_equal (g_type_name (type), "GdkPixbufSimpleAnim"))
     return;
 
-  /* Deprecated, not getting fixed */
-  if (g_str_equal (g_type_name (type), "GtkColorSelection") ||
-      g_str_equal (g_type_name (type), "GtkNumerableIcon"))
-    return;
-
   /* These can't be freely constructed/destroyed */
   if (g_type_is_a (type, GTK_TYPE_APPLICATION) ||
       g_type_is_a (type, GDK_TYPE_PIXBUF_LOADER) ||
@@ -396,36 +414,29 @@ test_type (gconstpointer data)
       g_str_equal (g_type_name (type), "GdkX11GLContext"))
     return;
 
-  /* This throws a critical when the connection is dropped */
-  if (g_type_is_a (type, GTK_TYPE_APP_CHOOSER_DIALOG))
-    return;
-
   /* These leak their GDBusConnections */
   if (g_type_is_a (type, GTK_TYPE_FILE_CHOOSER_DIALOG) ||
       g_type_is_a (type, GTK_TYPE_FILE_CHOOSER_WIDGET) ||
       g_type_is_a (type, GTK_TYPE_FILE_CHOOSER_NATIVE))
     return;
 
-  if (g_str_equal (g_type_name (type), "GtkPlacesSidebar"))
-    return;
-
   if (g_type_is_a (type, GTK_TYPE_STACK_PAGE))
     return;
 
-  /* These rely on a d-bus session bus */
-  if (g_type_is_a (type, GTK_TYPE_MOUNT_OPERATION))
-    return;
-
-  /* Needs a special surface */
-  if (g_type_is_a (type, GTK_TYPE_DRAG_ICON))
-    return;
-
   /* these assert in constructed */
  if (g_type_is_a (type, GTK_TYPE_ALTERNATIVE_TRIGGER) ||
      g_type_is_a (type, GTK_TYPE_SIGNAL_ACTION) ||
      g_type_is_a (type, GTK_TYPE_NAMED_ACTION))
     return;
 
+  /* needs a surface */
+  if (g_type_is_a (type, GTK_TYPE_DRAG_ICON))
+    return;
+
+  /* Needs debugging */
+  if (g_type_is_a (type, GTK_TYPE_SHORTCUTS_WINDOW))
+    return;
+
   klass = g_type_class_ref (type);
 
   if (g_type_is_a (type, GTK_TYPE_SETTINGS))
@@ -503,7 +514,7 @@ test_type (gconstpointer data)
       GParamSpec *pspec = pspecs[i];
 
       if ((pspec->flags & G_PARAM_READABLE) == 0)
-	continue;
+        continue;
 
       if ((pspec->flags & G_PARAM_WRITABLE) == 0)
         continue;
@@ -512,8 +523,8 @@ test_type (gconstpointer data)
         continue;
 
       /* non-GTK */
-      if (g_str_equal (g_type_name (pspec->owner_type), "GdkPixbufSimpleAnim") || 
-          g_str_equal (g_type_name (pspec->owner_type), "GMountOperation")) 
+      if (g_str_equal (g_type_name (pspec->owner_type), "GdkPixbufSimpleAnim") ||
+          g_str_equal (g_type_name (pspec->owner_type), "GMountOperation"))
         continue;
 
       /* set properties are best skipped */
@@ -547,11 +558,11 @@ test_type (gconstpointer data)
         continue;
 
       if (g_type_is_a (pspec->owner_type, GTK_TYPE_COLOR_CHOOSER) &&
-	  g_str_equal (pspec->name, "show-editor"))
+          g_str_equal (pspec->name, "show-editor"))
         continue;
 
       if (g_type_is_a (pspec->owner_type, GTK_TYPE_NOTEBOOK) &&
-	  g_str_equal (pspec->name, "page"))
+          g_str_equal (pspec->name, "page"))
         continue;
 
       /* Too many special cases involving -set properties */
@@ -593,7 +604,8 @@ test_type (gconstpointer data)
         continue;
 
       if (pspec->owner_type == GTK_TYPE_STACK &&
-          g_str_equal (pspec->name, "visible-child-name"))
+          (g_str_equal (pspec->name, "visible-child-name") ||
+           g_str_equal (pspec->name, "visible-child")))
         continue;
 
       if (pspec->owner_type == GTK_TYPE_STACK_PAGE && /* Can't change position without a stack */
@@ -623,51 +635,59 @@ test_type (gconstpointer data)
 
       /* This one has a special-purpose default value */
       if (g_type_is_a (type, GTK_TYPE_DIALOG) &&
-	  g_str_equal (pspec->name, "use-header-bar"))
-	continue;
+          g_str_equal (pspec->name, "use-header-bar"))
+        continue;
 
       if (g_type_is_a (type, GTK_TYPE_ASSISTANT) &&
-	  g_str_equal (pspec->name, "use-header-bar"))
-	continue;
+          g_str_equal (pspec->name, "use-header-bar"))
+        continue;
 
       if (g_type_is_a (type, GTK_TYPE_SHORTCUTS_SHORTCUT) &&
-	  g_str_equal (pspec->name, "accelerator"))
-	continue;
+          g_str_equal (pspec->name, "accelerator"))
+        continue;
 
       if (g_type_is_a (type, GTK_TYPE_SHORTCUT_LABEL) &&
-	  g_str_equal (pspec->name, "accelerator"))
-	continue;
+          g_str_equal (pspec->name, "accelerator"))
+        continue;
 
       if (g_type_is_a (type, GTK_TYPE_FONT_CHOOSER) &&
-	  g_str_equal (pspec->name, "font"))
-	continue;
+          g_str_equal (pspec->name, "font"))
+        continue;
 
       /* these depend on the min-content- properties in a way that breaks our test */
       if (g_type_is_a (type, GTK_TYPE_SCROLLED_WINDOW) &&
-	  (g_str_equal (pspec->name, "max-content-width") ||
-	   g_str_equal (pspec->name, "max-content-height")))
-	continue;
+          (g_str_equal (pspec->name, "max-content-width") ||
+           g_str_equal (pspec->name, "max-content-height")))
+        continue;
 
       /* expanding only works if rows are expandable */
       if (g_type_is_a (type, GTK_TYPE_TREE_LIST_ROW) &&
-	  g_str_equal (pspec->name, "expanded"))
-	continue;
+          g_str_equal (pspec->name, "expanded"))
+        continue;
 
-       /* can't select items without an underlying, populated model */
-       if (g_type_is_a (type, GTK_TYPE_SINGLE_SELECTION) &&
-           (g_str_equal (pspec->name, "selected") ||
-            g_str_equal (pspec->name, "selected-item")))
-         continue;
+      /* can't select items without an underlying, populated model */
+      if (g_type_is_a (type, GTK_TYPE_SINGLE_SELECTION) &&
+          (g_str_equal (pspec->name, "selected") ||
+           g_str_equal (pspec->name, "selected-item")))
+        continue;
 
-       /* can't select items without an underlying, populated model */
-       if (g_type_is_a (type, GTK_TYPE_DROP_DOWN) &&
-           g_str_equal (pspec->name, "selected"))
-         continue;
+      /* can't select items without an underlying, populated model */
+      if (g_type_is_a (type, GTK_TYPE_DROP_DOWN) &&
+          g_str_equal (pspec->name, "selected"))
+        continue;
 
        /* can't set position without a notebook */
-       if (g_type_is_a (type, GTK_TYPE_NOTEBOOK_PAGE) &&
-           g_str_equal (pspec->name, "position"))
-         continue;
+      if (g_type_is_a (type, GTK_TYPE_NOTEBOOK_PAGE) &&
+          g_str_equal (pspec->name, "position"))
+        continue;
+
+       /* This one is special */
+      if (g_str_equal (pspec->name, "focus-widget"))
+        continue;
+
+      if (pspec->owner_type == GTK_TYPE_TREE_VIEW_COLUMN &&
+          g_str_equal (pspec->name, "widget"))
+        continue;
 
       if (g_test_verbose ())
         g_print ("Property %s.%s\n", g_type_name (pspec->owner_type), pspec->name);