diff --git a/areas.cpp b/areas.cpp
index ea8c8f0..c557b53 100644
--- a/areas.cpp
+++ b/areas.cpp
@@ -69,7 +69,9 @@ Unit get_area_union(std::vector<Rectangle> rectangles) {
         //cross section is now up to date
         if(y_index + 1 < y_points.size()) {
             // add area up to next y point
-            total_area += segmentTree.length_covered_intervals();
+            total_area +=
+                    (y_points[y_index +1].coord - y_points[y_index].coord) *
+                    segmentTree.length_covered_intervals();
         }
     }
     // TODO: sanity check that nothing is covered when arriving at the end
diff --git a/main.cpp b/main.cpp
index 2e4afe2..6e4a85f 100644
--- a/main.cpp
+++ b/main.cpp
@@ -10,12 +10,12 @@ int main() {
     std::vector<Rectangle> rects;
     rects.push_back({{0,0},{10,10},0,0});
     Unit area = get_area_union(rects);
-    assert(area == 10);
+    assert(area == 100);
 
     rects.push_back({{2,3},{4,12},0,0});
     area = get_area_union(rects);
     std::cout << "Area is " << area << std::endl;
-    assert(area == 14);
+    assert(area == 104);
 
     std::vector<Rectangle> inst1 = get_random_instance(10,100);
     area = get_area_union(inst1);