diff --git a/src/viewport.cpp b/src/viewport.cpp
index 303e027600..3e4c2d273f 100644
--- a/src/viewport.cpp
+++ b/src/viewport.cpp
@@ -266,35 +266,36 @@ void InitializeWindowViewport(Window *w, int x, int y,
 
 static Point _vp_move_offs;
 
-static void DoSetViewportPosition(const Window *w, int left, int top, int width, int height)
+static void DoSetViewportPosition(Window::IteratorToFront it, int left, int top, int width, int height)
 {
-	for (const Window *w : Window::IterateFromBack(w)) {
+	for (; !it.IsEnd(); ++it) {
+		const Window *w = *it;
 		if (left + width > w->left &&
 				w->left + w->width > left &&
 				top + height > w->top &&
 				w->top + w->height > top) {
 
 			if (left < w->left) {
-				DoSetViewportPosition(w, left, top, w->left - left, height);
-				DoSetViewportPosition(w, left + (w->left - left), top, width - (w->left - left), height);
+				DoSetViewportPosition(it, left, top, w->left - left, height);
+				DoSetViewportPosition(it, left + (w->left - left), top, width - (w->left - left), height);
 				return;
 			}
 
 			if (left + width > w->left + w->width) {
-				DoSetViewportPosition(w, left, top, (w->left + w->width - left), height);
-				DoSetViewportPosition(w, left + (w->left + w->width - left), top, width - (w->left + w->width - left), height);
+				DoSetViewportPosition(it, left, top, (w->left + w->width - left), height);
+				DoSetViewportPosition(it, left + (w->left + w->width - left), top, width - (w->left + w->width - left), height);
 				return;
 			}
 
 			if (top < w->top) {
-				DoSetViewportPosition(w, left, top, width, (w->top - top));
-				DoSetViewportPosition(w, left, top + (w->top - top), width, height - (w->top - top));
+				DoSetViewportPosition(it, left, top, width, (w->top - top));
+				DoSetViewportPosition(it, left, top + (w->top - top), width, height - (w->top - top));
 				return;
 			}
 
 			if (top + height > w->top + w->height) {
-				DoSetViewportPosition(w, left, top, width, (w->top + w->height - top));
-				DoSetViewportPosition(w, left, top + (w->top + w->height - top), width, height - (w->top + w->height - top));
+				DoSetViewportPosition(it, left, top, width, (w->top + w->height - top));
+				DoSetViewportPosition(it, left, top + (w->top + w->height - top), width, height - (w->top + w->height - top));
 				return;
 			}
 
@@ -380,7 +381,11 @@ static void SetViewportPosition(Window *w, int x, int y)
 		i = top + height - _screen.height;
 		if (i >= 0) height -= i;
 
-		if (height > 0) DoSetViewportPosition(w->z_front, left, top, width, height);
+		if (height > 0) {
+			Window::IteratorToFront it(w);
+			++it;
+			DoSetViewportPosition(it, left, top, width, height);
+		}
 	}
 }
 
diff --git a/src/window.cpp b/src/window.cpp
index d6901bd97a..9b51eafd8a 100644
--- a/src/window.cpp
+++ b/src/window.cpp
@@ -896,7 +896,10 @@ static bool MayBeShown(const Window *w)
  */
 static void DrawOverlappedWindow(Window *w, int left, int top, int right, int bottom)
 {
-	for (const Window *v : Window::IterateFromBack(w->z_front)) {
+	Window::IteratorToFront it(w);
+	++it;
+	for (; !it.IsEnd(); ++it) {
+		const Window *v = *it;
 		if (MayBeShown(v) &&
 				right > v->left &&
 				bottom > v->top &&
@@ -2530,7 +2533,10 @@ static bool MaybeBringWindowToFront(Window *w)
 		w_height = w->unshaded_size.height;
 	}
 
-	for (Window *u : Window::IterateFromBack(w->z_front)) {
+	Window::IteratorToFront it(w);
+	++it;
+	for (; !it.IsEnd(); ++it) {
+		Window *u = *it;
 		/* A modal child will prevent the activation of the parent window */
 		if (u->parent == w && (u->window_desc->flags & WDF_MODAL)) {
 			u->SetWhiteBorder();
diff --git a/src/window_gui.h b/src/window_gui.h
index cf4ebcf73b..7f7ab2667e 100644
--- a/src/window_gui.h
+++ b/src/window_gui.h
@@ -833,39 +833,28 @@ public:
 		Window * operator*() const { return this->w; }
 		WindowIterator & operator++() { this->Next(); this->Validate(); return *this; }
 
+		bool IsEnd() const { return this->w == nullptr; }
+
 	private:
 		Window *w;
 		void Validate() { while (this->w != nullptr && this->w->window_class == WC_INVALID) this->Next(); }
 		void Next() { if (this->w != nullptr) this->w = Tfront ? this->w->z_back : this->w->z_front; }
 	};
+	using IteratorToFront = WindowIterator<false>; //!< Iterate in Z order towards front.
+	using IteratorToBack = WindowIterator<true>; //!< Iterate in Z order towards back.
 
 	/**
 	 * Iterable ensemble of all valid Windows
 	 * @tparam Tfront Wether we iterate from front
 	 */
 	template <bool Tfront>
-	struct Iterate {
-		Iterate(const Window *from) : from(from) {}
-		WindowIterator<Tfront> begin() { return WindowIterator<Tfront>(this->from); }
+	struct AllWindows {
+		AllWindows() {}
+		WindowIterator<Tfront> begin() { return WindowIterator<Tfront>(Tfront ? _z_front_window : _z_back_window); }
 		WindowIterator<Tfront> end() { return WindowIterator<Tfront>(nullptr); }
-		bool empty() { return this->begin() == this->end(); }
-	private:
-		const Window *from;
 	};
-
-	/**
-	 * Returns an iterable ensemble of all valid Window from back to front
-	 * @param from index of the first Window to consider
-	 * @return an iterable ensemble of all valid Window
-	 */
-	static Iterate<false> IterateFromBack(const Window *from = _z_back_window) { return Iterate<false>(from); }
-
-	/**
-	 * Returns an iterable ensemble of all valid Window from front to back
-	 * @param from index of the first Window to consider
-	 * @return an iterable ensemble of all valid Window
-	 */
-	static Iterate<true> IterateFromFront(const Window *from = _z_front_window) { return Iterate<true>(from); }
+	using IterateFromBack = AllWindows<false>; //!< Iterate all windows in Z order from back to front.
+	using IterateFromFront = AllWindows<true>; //!< Iterate all windows in Z order from front to back.
 };
 
 /**