--- a/src/widget.cpp
+++ b/src/widget.cpp
@@ -839,6 +839,13 @@
  */
 
 /**
+ * @fn void FillNestedArray(NWidgetCore **array, uint length)
+ * Fill the Window::nested_array array with pointers to nested widgets in the tree.
+ * @param array Base pointer of the array.
+ * @param length Length of the array.
+ */
+
+/**
  * Store size and position.
  * @param sizing         Type of resizing to perform.
  * @param x              Horizontal offset of the widget relative to the left edge of the window.
@@ -971,6 +978,11 @@
 	return this->index;
 }
 
+void NWidgetCore::FillNestedArray(NWidgetCore **array, uint length)
+{
+	if (this->index >= 0 && (uint)(this->index) < length) array[this->index] = this;
+}
+
 void NWidgetCore::StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl)
 {
 	if (this->index < 0) return;
@@ -1046,6 +1058,13 @@
 	}
 }
 
+void NWidgetContainer::FillNestedArray(NWidgetCore **array, uint length)
+{
+	for (NWidgetBase *child_wid = this->head; child_wid != NULL; child_wid = child_wid->next) {
+		child_wid->FillNestedArray(array, length);
+	}
+}
+
 /**
  * Return the biggest possible size of a nested widget.
  * @param base      Base size of the widget.
@@ -1419,6 +1438,10 @@
 	return -1;
 }
 
+void NWidgetSpacer::FillNestedArray(NWidgetCore **array, uint length)
+{
+}
+
 void NWidgetSpacer::StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl)
 {
 	/* Spacer widgets are never stored in the widget array. */
@@ -1518,6 +1541,12 @@
 	if (this->child != NULL) this->child->StoreWidgets(widgets, length, left_moving, top_moving, rtl);
 }
 
+void NWidgetBackground::FillNestedArray(NWidgetCore **array, uint length)
+{
+	if (this->index >= 0 && (uint)(this->index) < length) array[this->index] = this;
+	if (this->child != NULL) this->child->FillNestedArray(array, length);
+}
+
 /**
  * Nested leaf widget.
  * @param tp     Type of leaf widget.

--- a/src/widget_type.h
+++ b/src/widget_type.h
@@ -151,6 +151,9 @@
 	ST_RESIZE,   ///< Resize the nested widget tree.
 };
 
+/* Forward declarations. */
+class NWidgetCore;
+
 /**
  * Baseclass for nested widgets.
  * @invariant After initialization, \f$current\_x = smallest\_x + n * resize\_x, for n \geq 0\f$.
@@ -165,6 +168,7 @@
 	virtual void AssignSizePosition(SizingType sizing, uint x, uint y, uint given_width, uint given_height, bool allow_resize_x, bool allow_resize_y, bool rtl) = 0;
 
 	virtual void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl) = 0;
+	virtual void FillNestedArray(NWidgetCore **array, uint length) = 0;
 
 	/**
 	 * Set additional space (padding) around the widget.
@@ -260,6 +264,7 @@
 
 	int SetupSmallestSize();
 	void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl);
+	/* virtual */ void FillNestedArray(NWidgetCore **array, uint length);
 
 	Colours colour;     ///< Colour of this widget.
 	int index;          ///< Index of the nested widget in the widget array of the window (\c -1 means 'not used').
@@ -275,6 +280,7 @@
 	~NWidgetContainer();
 
 	void Add(NWidgetBase *wid);
+	/* virtual */ void FillNestedArray(NWidgetCore **array, uint length);
 
 	/** Return whether the container is empty. */
 	inline bool IsEmpty() { return head == NULL; };
@@ -353,6 +359,7 @@
 
 	int SetupSmallestSize();
 	void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl);
+	/* virtual */ void FillNestedArray(NWidgetCore **array, uint length);
 };
 
 /** Nested widget with a child.
@@ -369,6 +376,8 @@
 	void AssignSizePosition(SizingType sizing, uint x, uint y, uint given_width, uint given_height, bool allow_resize_x, bool allow_resize_y, bool rtl);
 
 	void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl);
+	/* virtual */ void FillNestedArray(NWidgetCore **array, uint length);
+
 private:
 	NWidgetPIPContainer *child; ///< Child widget.
 };

--- a/src/window.cpp
+++ b/src/window.cpp
@@ -563,6 +563,8 @@
 	this->SetDirty();
 
 	free(this->widget);
+	free(this->nested_array); // Contents is released through deletion of #nested_root.
+	delete this->nested_root;
 
 	this->window_class = WC_INVALID;
 }
@@ -789,6 +791,8 @@
 void Window::Initialize(int x, int y, int min_width, int min_height,
 				WindowClass cls, const Widget *widget, int window_number)
 {
+	/* All data members of nested widgets have been set to 0 by the #ZeroedMemoryAllocator base class. */
+
 	/* Set up window properties */
 	this->window_class = cls;
 	this->flags4 = WF_WHITE_BORDER_MASK; // just opened windows have a white border

--- a/src/window_gui.h
+++ b/src/window_gui.h
@@ -169,11 +169,14 @@
 
 	Owner owner;        ///< The owner of the content shown in this window. Company colour is acquired from this variable.
 
-	ViewportData *viewport;///< Pointer to viewport data, if present
-	Widget *widget;        ///< Widgets of the window
-	uint widget_count;     ///< Number of widgets of the window
-	uint32 desc_flags;     ///< Window/widgets default flags setting, @see WindowDefaultFlag
-	const Widget *focused_widget; ///< Currently focused widget or NULL, if no widget has focus
+	ViewportData *viewport;       ///< Pointer to viewport data, if present.
+	Widget *widget;               ///< Widgets of the window.
+	uint widget_count;            ///< Number of widgets of the window.
+	uint32 desc_flags;            ///< Window/widgets default flags setting. @see WindowDefaultFlag
+	const Widget *focused_widget; ///< Currently focused widget, or \c NULL if no widget has focus.
+	NWidgetBase *nested_root;     ///< Root of the nested tree.
+	NWidgetCore **nested_array;   ///< Array of pointers into the tree.
+	uint nested_array_size;       ///< Size of the nested array.
 
 	Window *parent;        ///< Parent window
 	Window *z_front;       ///< The window in front of us in z-order