diff --git a/rocketpy/mathutils/function.py b/rocketpy/mathutils/function.py
index 9e6e07b9d..945d36d26 100644
--- a/rocketpy/mathutils/function.py
+++ b/rocketpy/mathutils/function.py
@@ -3171,7 +3171,7 @@ def savetxt(
                 )
             # Generate the data points using the callable
             x = np.linspace(lower, upper, samples)
-            data_points = np.column_stack((x, self.source(x)))
+            data_points = np.column_stack((x, self.get_value_opt(x)))
         else:
             # If the source is already an array, use it as is
             data_points = self.source