diff --git a/src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp b/src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp
index 619cebb79..9c65f18eb 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp
@@ -151,9 +151,9 @@ void GLGizmoFlatten::update_planes()
     std::vector<bool>        facet_visited(num_of_facets, false);
     int                      facet_queue_cnt = 0;
     const stl_normal*        normal_ptr      = nullptr;
+    int                      facet_idx       = 0;
     while (1) {
         // Find next unvisited triangle:
-        int facet_idx = 0;
         for (; facet_idx < num_of_facets; ++ facet_idx)
             if (!facet_visited[facet_idx]) {
                 facet_queue[facet_queue_cnt ++] = facet_idx;
@@ -250,7 +250,8 @@ void GLGizmoFlatten::update_planes()
         }
 
         if (discard) {
-            m_planes.erase(m_planes.begin() + (polygon_id--));
+            m_planes[polygon_id--] = std::move(m_planes.back());
+            m_planes.pop_back();
             continue;
         }