diff --git a/src/physics.F90 b/src/physics.F90
index 1bc7e4729..982584844 100644
--- a/src/physics.F90
+++ b/src/physics.F90
@@ -51,6 +51,13 @@ contains
       call sample_positron_reaction(p)
     end if
 
+    ! Kill particle if energy falls below cutoff
+    if (p % E < energy_cutoff(p % type)) then
+      p % alive = .false.
+      p % wgt = ZERO
+      p % last_wgt = ZERO
+    end if
+
     ! Display information about collision
     if (verbosity >= 10 .or. trace) then
       if (p % type == NEUTRON) then
@@ -170,7 +177,9 @@ contains
     real(8) :: uvw(3)       ! new direction
     real(8) :: rel_vel      ! relative velocity of electron
 
-    ! Kill photon if below energy cutoff
+    ! Kill photon if below energy cutoff -- an extra check is made here because
+    ! photons with energy below the cutoff may have been produced by neutrons
+    ! reactions or atomic relaxation
     if (p % E < energy_cutoff(PHOTON)) then
       p % E = ZERO
       p % alive = .false.