diff --git a/src/viewport.cpp b/src/viewport.cpp
--- a/src/viewport.cpp
+++ b/src/viewport.cpp
@@ -165,6 +165,9 @@ static Point MapXYZToViewport(const View
 
 void DeleteWindowViewport(Window *w)
 {
+	if (w->viewport == NULL) return;
+
+	delete w->viewport->overlay;
 	free(w->viewport);
 	w->viewport = NULL;
 }