diff --git a/src/collision/collision_regime.f90 b/src/collision/collision_regime.f90
index 50884258b..ac571b23c 100644
--- a/src/collision/collision_regime.f90
+++ b/src/collision/collision_regime.f90
@@ -36,9 +36,9 @@ module subroutine collision_regime_impactors(self, nbody_system, param)
          case("MERGE")
             impactors%regime = COLLRESOLVE_REGIME_MERGE
             mtot = sum(impactors%mass(:))
+            if (allocated(impactors%mass_dist)) deallocate(impactors%mass_dist)
+            allocate(impactors%mass_dist(1))
             impactors%mass_dist(1) = mtot
-            impactors%mass_dist(2) = 0.0_DP
-            impactors%mass_dist(3) = 0.0_DP
             impactors%rbcom(:) = (impactors%mass(1) * impactors%rb(:,1) + impactors%mass(2) * impactors%rb(:,2)) / mtot
             impactors%vbcom(:) = (impactors%mass(1) * impactors%vb(:,1) + impactors%mass(2) * impactors%vb(:,2)) / mtot
          case default