diff --git a/dw/types.cc b/dw/types.cc
index e49847c..be27005 100644
--- a/dw/types.cc
+++ b/dw/types.cc
@@ -231,8 +231,14 @@ void Region::addRectangle (Rectangle *rPointer)
    auto r= std::make_unique< Rectangle >( rPointer->x, rPointer->y,
       rPointer->width, rPointer->height );
 
-   for( auto &ownRect: rectangleList )
+   for( auto it= rectangleList.begin(); it != rectangleList.end(); )
    {
+      // We have to increment immediately.  The removal of the element, near the bottom
+      // of this loop will invalidate any iterators pointing into the rectangleList at
+      // that position.  A range-based for loop will increment the iterator after the
+      // current pass, which would cause crashes.
+      auto &ownRect= *it++;
+
       int combinedHeight =
          misc::max(r->y + r->height, ownRect->y + ownRect->height) -
          misc::min(r->y, ownRect->y);