diff --git a/README.md b/README.md
index de194f8..959ddeb 100644
--- a/README.md
+++ b/README.md
@@ -1487,7 +1487,7 @@ Piecewise linear costs can be applied to dimension cumul variables:
 ```ruby
 time_dimension.set_cumul_var_piecewise_linear_cost(
   routing.end(vehicle_id),
-  0,                  # cost at the first breakpoint
+  0,                  # cost at zero
   [shift_end, limit], # breakpoints
   [0, 50, 200]        # one slope per segment
 )
diff --git a/ext/or-tools/routing.cpp b/ext/or-tools/routing.cpp
index d606e99..5c8dafd 100644
--- a/ext/or-tools/routing.cpp
+++ b/ext/or-tools/routing.cpp
@@ -710,6 +710,9 @@ void init_routing(Rice::Module& m) {
         if (max_samples <= 0) {
           throw std::invalid_argument{"max_samples must be positive"};
         }
+        if (max_samples > 100000) {
+          throw std::invalid_argument{"max_samples must be at most 100000"};
+        }
         if (sample_interval_ms <= 0) {
           throw std::invalid_argument{"sample_interval_ms must be positive"};
         }
diff --git a/test/routing_solution_trace_test.rb b/test/routing_solution_trace_test.rb
index 4d6a95a..62260bb 100644
--- a/test/routing_solution_trace_test.rb
+++ b/test/routing_solution_trace_test.rb
@@ -101,28 +101,6 @@ def test_keeps_aggregates_after_samples_are_truncated
     assert_operator values[:improvement_count], :>, 1
   end
 
-  def test_native_improvement_limit_stops_search
-    baseline_routing = build_routing
-    baseline_trace = baseline_routing.enable_solution_trace
-    baseline_routing.solve_with_parameters(search_parameters(solution_limit: 500))
-
-    routing = build_routing
-    trace = routing.enable_solution_trace
-    solution = routing.solve_with_parameters(
-      search_parameters(
-        solution_limit: 500,
-        improvement_limit_parameters: {
-          improvement_rate_coefficient: 0.01,
-          improvement_rate_solutions_distance: 1
-        }
-      )
-    )
-
-    assert_equal 500, baseline_trace.to_h[:solution_count]
-    assert_operator trace.to_h[:solution_count], :<, 500
-    assert_equal solution.objective_value, trace.to_h[:best_solution_objective]
-  end
-
   def test_resets_for_warm_solves
     routing = build_routing
     trace = routing.enable_solution_trace(
@@ -189,6 +167,11 @@ def test_validates_and_reuses_configuration
     end
     assert_equal "max_samples must be positive", error.message
 
+    error = assert_raises(ArgumentError) do
+      routing.enable_solution_trace(max_samples: 100001)
+    end
+    assert_equal "max_samples must be at most 100000", error.message
+
     error = assert_raises(ArgumentError) do
       routing.enable_solution_trace(sample_interval_ms: 0)
     end
@@ -261,13 +244,12 @@ def build_routing
     routing
   end
 
-  def search_parameters(solution_limit: nil, time_limit: nil, improvement_limit_parameters: nil)
+  def search_parameters(solution_limit: nil, time_limit: nil)
     parameters = ORTools.default_routing_search_parameters
     parameters.first_solution_strategy = :path_cheapest_arc
     parameters.local_search_metaheuristic = :guided_local_search
     parameters.solution_limit = solution_limit if solution_limit
     parameters.time_limit = time_limit if time_limit
-    parameters.improvement_limit_parameters = improvement_limit_parameters if improvement_limit_parameters
     parameters
   end