diff --git a/lib/or_tools/cp_solver_solution_callback.rb b/lib/or_tools/cp_solver_solution_callback.rb
index c71509a..29bc3ba 100644
--- a/lib/or_tools/cp_solver_solution_callback.rb
+++ b/lib/or_tools/cp_solver_solution_callback.rb
@@ -5,16 +5,16 @@ class CpSolverSolutionCallback
     def value(expr)
       case expr
       when SatIntVar
-        @response.solution_integer_value(expr)
+        @response&.solution_integer_value(expr)
       when BoolVar
-        @response.solution_boolean_value(expr)
+        @response&.solution_boolean_value(expr)
       else
         raise "Unsupported type: #{expr.class.name}"
       end
     end
 
     def objective_value
-      @response.objective_value
+      @response&.objective_value
     end
   end
 end
diff --git a/test/solution_printer_test.rb b/test/solution_printer_test.rb
index aca63b2..e3129c0 100644
--- a/test/solution_printer_test.rb
+++ b/test/solution_printer_test.rb
@@ -10,11 +10,17 @@ def test_objective_solution_printer
     solver = ORTools::CpSolver.new
     solver.parameters.enumerate_all_solutions = true
     solution_printer = ORTools::ObjectiveSolutionPrinter.new
+    assert_nil solution_printer.objective_value
+
     stdout, _ = capture_io do
       solver.solve(model, solution_printer)
     end
     assert_equal 15, solution_printer.solution_count
     assert_match "Solution 14", stdout
+
+    # ensure @response is still valid after solve
+    GC.start
+    assert_equal 0, solution_printer.objective_value
   end
 
   def test_var_array_solution_printer