diff --git a/src/libslic3r/Fill/Fill.cpp b/src/libslic3r/Fill/Fill.cpp
index 5760073d8..4804107cd 100644
--- a/src/libslic3r/Fill/Fill.cpp
+++ b/src/libslic3r/Fill/Fill.cpp
@@ -359,6 +359,7 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
 
 	// BBS: detect narrow internal solid infill area and use ipConcentricInternal pattern instead
 	if (layer.object()->config().detect_narrow_internal_solid_infill) {
+		const coordf_t narrow_threshold = scale_(NARROW_INFILL_AREA_THRESHOLD) * 2;
 		ExPolygons lower_internal_areas;
 		BoundingBox lower_internal_bbox;
 		if (layer.lower_layer) {
@@ -381,8 +382,10 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
 			// BBS: get the index list of narrow expolygon
 			for (size_t j = 0; j < expolygons_size; j++) {
 				auto bbox = get_extents(surface_fills[i].expolygons[j]);
-				if (is_narrow_expolygon(surface_fills[i].expolygons[j], scale_(NARROW_INFILL_AREA_THRESHOLD) * 2)) {
-					if (bbox.overlap(lower_internal_bbox) && !intersection_ex(offset_ex(surface_fills[i].expolygons[j],SCALED_EPSILON), lower_internal_areas).empty()) {
+				auto clipped_internals = ClipperUtils::clip_clipper_polygons_with_subject_bbox(lower_internal_areas, bbox.inflated(scale_(2))); // expand a little
+				auto clipped_internal_bbox = get_extents(clipped_internals);
+				if (is_narrow_expolygon(surface_fills[i].expolygons[j], narrow_threshold)) {
+					if (!clipped_internals.empty() && bbox.overlap(clipped_internal_bbox) && !intersection_ex(offset_ex(surface_fills[i].expolygons[j],SCALED_EPSILON), clipped_internals).empty()) {
 						narrow_floating_expoly_idx.emplace_back(j);
 					}
 					else {
diff --git a/src/slic3r/GUI/ConfigManipulation.cpp b/src/slic3r/GUI/ConfigManipulation.cpp
index 15a2a03f5..e797a3f45 100644
--- a/src/slic3r/GUI/ConfigManipulation.cpp
+++ b/src/slic3r/GUI/ConfigManipulation.cpp
@@ -651,8 +651,8 @@ void ConfigManipulation::toggle_print_fff_options(DynamicPrintConfig *config, in
         toggle_line(el, support_is_tree);
     toggle_line("support_critical_regions_only", is_auto(support_type) && support_is_tree);
 
-    for (auto el : { "detect_floating_vertical_shell", "vertical_shell_speed" })
-        toggle_line(el, config->option<ConfigOptionEnum<EnsureVerticalThicknessLevel>>("ensure_vertical_shell_thickness")->value != EnsureVerticalThicknessLevel::evtDisabled);
+    toggle_line("detect_floating_vertical_shell", config->option<ConfigOptionBool>("detect_narrow_internal_solid_infill")->value);
+    toggle_line("vertical_shell_speed", config->option<ConfigOptionBool>("detect_narrow_internal_solid_infill")->value, variant_index);
 
     // tree support use max_bridge_length instead of bridge_no_support
     toggle_line("bridge_no_support", !support_is_tree);