diff --git a/src/libslic3r/GCode.cpp b/src/libslic3r/GCode.cpp
index dfd7ab0fb..972f62ca8 100644
--- a/src/libslic3r/GCode.cpp
+++ b/src/libslic3r/GCode.cpp
@@ -4249,11 +4249,14 @@ static std::map<int, std::string> overhang_speed_key_map =
 
 double GCode::get_overhang_degree_corr_speed(float normal_speed, double path_degree) {
 
-    if (path_degree== 0)
+    //BBS: protection: overhang degree is float, make sure it not excess degree range
+    if (path_degree <= 0)
         return normal_speed;
 
-    int lower_degree_bound = int(path_degree);
+    if (path_degree >= 5 )
+        return m_config.get_abs_value(overhang_speed_key_map[5].c_str());
 
+    int lower_degree_bound = int(path_degree);
     if (path_degree==lower_degree_bound)
         return m_config.get_abs_value(overhang_speed_key_map[lower_degree_bound].c_str());
     int upper_degree_bound = lower_degree_bound + 1;
diff --git a/src/libslic3r/PerimeterGenerator.cpp b/src/libslic3r/PerimeterGenerator.cpp
index 3b07f38f9..26d97a2d4 100644
--- a/src/libslic3r/PerimeterGenerator.cpp
+++ b/src/libslic3r/PerimeterGenerator.cpp
@@ -13,6 +13,7 @@
 static const int overhang_sampling_number = 6;
 static const double narrow_loop_length_threshold = 10;
 static const double min_degree_gap = 0.1;
+static const int max_overhang_degree = overhang_sampling_number - 1;
 //BBS: when the width of expolygon is smaller than
 //ext_perimeter_width + ext_perimeter_spacing  * (1 - SMALLER_EXT_INSET_OVERLAP_TOLERANCE),
 //we think it's small detail area and will generate smaller line width for it
@@ -231,6 +232,7 @@ static std::deque<PolylineWithDegree> split_polyline_by_degree(const Polyline &p
     // BBS: merge degree in limited range
     //find first degee base
     double degree_base = int(points_overhang[points_overhang.size() - 1] / min_degree_gap) * min_degree_gap + min_degree_gap;
+    degree_base = degree_base > max_overhang_degree ? max_overhang_degree : degree_base;
     double short_poly_len = 0;
     for (int point_idx = points_overhang.size() - 2; point_idx > 0; --point_idx) {
 
@@ -245,7 +247,7 @@ static std::deque<PolylineWithDegree> split_polyline_by_degree(const Polyline &p
         out.push_back(PolylineWithDegree(right, degree_base));
 
         degree_base = int(degree / min_degree_gap) * min_degree_gap + min_degree_gap;
-        degree_base = degree_base > overhang_sampling_number - 2 ? overhang_sampling_number - 2 : degree_base;
+        degree_base = degree_base > max_overhang_degree ? max_overhang_degree : degree_base;
     }
 
     if (!temp_copy.empty()) {
@@ -356,7 +358,7 @@ static std::deque<PolylineWithDegree> detect_overahng_degree(Polygons        low
             float overhang_dist = prev_layer_distancer->distance_from_perimeter(pt.cast<float>());
             overhang_dist       = overhang_dist > upper_bound ? upper_bound : overhang_dist;
             // BBS : calculate overhang degree
-            int    max_overhang = overhang_sampling_number - 2;
+            int    max_overhang = max_overhang_degree;
             int    min_overhang = 0;
             double t            = (overhang_dist - lower_bound) / (upper_bound - lower_bound);
             t = t > 1.0 ? 1: t;