diff --git a/main.cpp b/main.cpp
index a7b7703..c89a89a 100644
--- a/main.cpp
+++ b/main.cpp
@@ -22,10 +22,10 @@ int main() {
     srand(987192345);
 
     add_rect(0,0,5,4);
-    check_area(20);
+  //  check_area(20);
 
     add_rect(3,2,6,6);
-    check_area(28);
+//    check_area(28);
 
     add_rect(1,-2,8,4);
     check_area(52);
diff --git a/segment_tree.h b/segment_tree.h
index 2ee53d3..2d399e3 100644
--- a/segment_tree.h
+++ b/segment_tree.h
@@ -72,7 +72,9 @@ void SegmentTree::add_coverage(Index node_idx) {
 
 void SegmentTree::remove_coverage(Index node_idx) {
     --(_nodes[node_idx].coverage);
-    update_covered_length(node_idx);
+    if(!_nodes[node_idx].covered()) {
+        update_covered_length(node_idx);
+    }
 }
 
 Index SegmentTree::left_child_idx(Index node_idx) {
@@ -84,6 +86,7 @@ Index SegmentTree::right_child_idx(Index node_idx) {
 }
 
 void SegmentTree::update_covered_length(Index node_idx) {
+    assert(!_nodes[node_idx].covered());
     if (is_leaf(node_idx)) {
         _nodes[node_idx].covered_length = 0;
     } else {