diff --git a/src/libslic3r/PrintObject.cpp b/src/libslic3r/PrintObject.cpp
index 273fc9c10..0f1a91a92 100644
--- a/src/libslic3r/PrintObject.cpp
+++ b/src/libslic3r/PrintObject.cpp
@@ -2823,8 +2823,9 @@ void PrintObject::project_and_append_custom_supports(
         // Now append the collected polygons to respective layers.
         for (auto& trg : projections_of_triangles) {
             int layer_id = trg.first_layer_id;
-
             for (const LightPolygon& poly : trg.polygons) {
+                if (layer_id >= int(expolys.size()))
+                    break; // part of triangle could be projected above top layer
                 expolys[layer_id].emplace_back(std::move(poly.pts));
                 ++layer_id;
             }
diff --git a/src/libslic3r/TriangleSelector.cpp b/src/libslic3r/TriangleSelector.cpp
index 763bf5861..9555c42a6 100644
--- a/src/libslic3r/TriangleSelector.cpp
+++ b/src/libslic3r/TriangleSelector.cpp
@@ -60,8 +60,9 @@ void TriangleSelector::select_patch(const Vec3f& hit, int facet_start,
             if (select_triangle(facet, new_state)) {
                 // add neighboring facets to list to be proccessed later
                 for (int n=0; n<3; ++n) {
-                    if (faces_camera(m_mesh->stl.neighbors_start[facet].neighbor[n]))
-                        facets_to_check.push_back(m_mesh->stl.neighbors_start[facet].neighbor[n]);
+                    int neighbor_idx = m_mesh->stl.neighbors_start[facet].neighbor[n];
+                    if (neighbor_idx >=0 && faces_camera(neighbor_idx))
+                        facets_to_check.push_back(neighbor_idx);
                 }
             }
         }