diff --git a/source/world_builder/features/subducting_plate_models/temperature/mass_conserving.cc b/source/world_builder/features/subducting_plate_models/temperature/mass_conserving.cc
index e7f14142e..e497729a4 100644
--- a/source/world_builder/features/subducting_plate_models/temperature/mass_conserving.cc
+++ b/source/world_builder/features/subducting_plate_models/temperature/mass_conserving.cc
@@ -276,9 +276,9 @@ namespace WorldBuilder
                                                      subducting_velocities,
                                                      ridge_spreading_velocities.first);
 
-              const double km2m = 1.0e3; // 1000 m/km
-              const double cm2m = 100; // 100 cm/m
-              const double my = 1.0e6;  // 1e6 y/my
+              constexpr double km2m = 1.0e3; // 1000 m/km
+              constexpr double cm2m = 100; // 100 cm/m
+              constexpr double my = 1.0e6;  // 1e6 y/my
 
               /* information about nearest point on the slab segment */
               const double distance_along_plane = distance_from_planes.distance_along_plane;
diff --git a/source/world_builder/utilities.cc b/source/world_builder/utilities.cc
index e581e4b33..55285a855 100644
--- a/source/world_builder/utilities.cc
+++ b/source/world_builder/utilities.cc
@@ -1473,7 +1473,8 @@ namespace WorldBuilder
 
       // Plate age increases with distance along the slab in the mantle
       double effective_plate_age = plate_age_sec + (distance_along_plane / subducting_velocity + effective_age_shift) * seconds_in_year; // m/(m/y) = y(seconds_in_year)
-
+      WBAssertThrow(effective_plate_age >= 0, "The age of the subducting plate is less than or equal to 0. "
+                    "Effective plate age: " << effective_plate_age);
       std::vector<double> result;
       result.push_back(age_at_trench);
       result.push_back(effective_plate_age);