diff --git a/src/libslic3r/GCode/CoolingBuffer.cpp b/src/libslic3r/GCode/CoolingBuffer.cpp
index ff36ce7e21..2f4938bc7a 100644
--- a/src/libslic3r/GCode/CoolingBuffer.cpp
+++ b/src/libslic3r/GCode/CoolingBuffer.cpp
@@ -521,62 +521,6 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
     return per_extruder_adjustments;
 }
 
-// Slow down an extruder range proportionally down to slow_down_layer_time.
-// Return the total time for the complete layer.
-static inline float extruder_range_slow_down_proportional(
-    std::vector<PerExtruderAdjustments*>::iterator it_begin,
-    std::vector<PerExtruderAdjustments*>::iterator it_end,
-    // Elapsed time for the extruders already processed.
-    float elapsed_time_total0,
-    // Initial total elapsed time before slow down.
-    float elapsed_time_before_slowdown,
-    // Target time for the complete layer (all extruders applied).
-    float slow_down_layer_time)
-{
-    // Total layer time after the slow down has been applied.
-    float total_after_slowdown = elapsed_time_before_slowdown;
-    // Now decide, whether the external perimeters shall be slowed down as well.
-    float max_time_nep = elapsed_time_total0;
-    for (auto it = it_begin; it != it_end; ++ it)
-        max_time_nep += (*it)->maximum_time_after_slowdown(false);
-    if (max_time_nep > slow_down_layer_time) {
-        // It is sufficient to slow down the non-external perimeter moves to reach the target layer time.
-        // Slow down the non-external perimeters proportionally.
-        float non_adjustable_time = elapsed_time_total0;
-        for (auto it = it_begin; it != it_end; ++ it)
-            non_adjustable_time += (*it)->non_adjustable_time(false);
-        // The following step is a linear programming task due to the minimum movement speeds of the print moves.
-        // Run maximum 5 iterations until a good enough approximation is reached.
-        for (size_t iter = 0; iter < 5; ++ iter) {
-            float factor = (slow_down_layer_time - non_adjustable_time) / (total_after_slowdown - non_adjustable_time);
-            assert(factor > 1.f);
-            total_after_slowdown = elapsed_time_total0;
-            for (auto it = it_begin; it != it_end; ++ it)
-                total_after_slowdown += (*it)->slow_down_proportional(factor, false);
-            if (total_after_slowdown > 0.95f * slow_down_layer_time)
-                break;
-        }
-    } else {
-        // Slow down everything. First slow down the non-external perimeters to maximum.
-        for (auto it = it_begin; it != it_end; ++ it)
-            (*it)->slowdown_to_minimum_feedrate(false);
-        // Slow down the external perimeters proportionally.
-        float non_adjustable_time = elapsed_time_total0;
-        for (auto it = it_begin; it != it_end; ++ it)
-            non_adjustable_time += (*it)->non_adjustable_time(true);
-        for (size_t iter = 0; iter < 5; ++ iter) {
-            float factor = (slow_down_layer_time - non_adjustable_time) / (total_after_slowdown - non_adjustable_time);
-            assert(factor > 1.f);
-            total_after_slowdown = elapsed_time_total0;
-            for (auto it = it_begin; it != it_end; ++ it)
-                total_after_slowdown += (*it)->slow_down_proportional(factor, true);
-            if (total_after_slowdown > 0.95f * slow_down_layer_time)
-                break;
-        }
-    }
-    return total_after_slowdown;
-}
-
 // Slow down an extruder range to slow_down_layer_time.
 // Return the total time for the complete layer.
 static inline void extruder_range_slow_down_non_proportional(
@@ -674,9 +618,8 @@ float CoolingBuffer::calculate_layer_slowdown(std::vector<PerExtruderAdjustments
         adj.time_maximum = adj.maximum_time_after_slowdown(true);
         if (adj.cooling_slow_down_enabled && adj.lines.size() > 0) {
             by_slowdown_time.emplace_back(&adj);
-            if (! m_cooling_logic_proportional)
-                // sorts the lines, also sets adj.time_non_adjustable
-                adj.sort_lines_by_decreasing_feedrate();
+            // sorts the lines, also sets adj.time_non_adjustable
+            adj.sort_lines_by_decreasing_feedrate();
         } else
             elapsed_time_total0 += adj.elapsed_time_total();
     }
@@ -700,10 +643,7 @@ float CoolingBuffer::calculate_layer_slowdown(std::vector<PerExtruderAdjustments
             for (auto it = cur_begin; it != by_slowdown_time.end(); ++ it)
                 max_time += (*it)->time_maximum;
             if (max_time > slow_down_layer_time) {
-                if (m_cooling_logic_proportional)
-                    extruder_range_slow_down_proportional(cur_begin, by_slowdown_time.end(), elapsed_time_total0, total, slow_down_layer_time);
-                else
-                    extruder_range_slow_down_non_proportional(cur_begin, by_slowdown_time.end(), slow_down_layer_time - total);
+                extruder_range_slow_down_non_proportional(cur_begin, by_slowdown_time.end(), slow_down_layer_time - total);
             } else {
                 // Slow down to maximum possible.
                 for (auto it = cur_begin; it != by_slowdown_time.end(); ++ it)
diff --git a/src/libslic3r/GCode/CoolingBuffer.hpp b/src/libslic3r/GCode/CoolingBuffer.hpp
index 7fb55985f7..dcbf0120b8 100644
--- a/src/libslic3r/GCode/CoolingBuffer.hpp
+++ b/src/libslic3r/GCode/CoolingBuffer.hpp
@@ -54,9 +54,6 @@ private:
     // the PrintConfig slice of FullPrintConfig is constant, thus no thread synchronization is required.
     const PrintConfig          &m_config;
     unsigned int                m_current_extruder;
-
-    // Old logic: proportional.
-    bool                        m_cooling_logic_proportional = false;
     //BBS: current fan speed
     int                         m_current_fan_speed;
 };