diff --git a/pyHalo/realization_extensions.py b/pyHalo/realization_extensions.py
index 11c2194..68623ff 100644
--- a/pyHalo/realization_extensions.py
+++ b/pyHalo/realization_extensions.py
@@ -51,6 +51,8 @@ def add_prompt_cusps(self, mass_fraction):
                                     halo.z, halo.is_subhalo, halo.lens_cosmo,
                                     args, halo._truncation_class, halo._concentration_class,
                                     halo.unique_tag)
+            if halo.is_subhalo:
+                prompt_cusp.set_bound_mass(halo.bound_mass)
             halo._rescale_norm *= (1 - mass_fraction)
             halo_list.append(halo)
             halo_list.append(prompt_cusp)