diff --git a/src/input_xml.F90 b/src/input_xml.F90
index cf52075721..91cd57ae29 100644
--- a/src/input_xml.F90
+++ b/src/input_xml.F90
@@ -2341,17 +2341,20 @@ contains
 
       if (run_CE) then
         ! By default, isotropic-in-lab is not used
-        allocate(mat % p0(n))
-        mat % p0(:) = .false.
+        if (list_iso_lab % size() > 0) then
+          mat % has_isotropic_nuclides = .true.
+          allocate(mat % p0(n))
+          mat % p0(:) = .false.
 
-        ! Apply isotropic-in-lab treatment to specified nuclides
-        do j = 1, list_iso_lab % size()
-          do k = 1, n
-            if (names % data(k) == list_iso_lab % data(j)) then
-              mat % p0(k) = .true.
-            end if
+          ! Apply isotropic-in-lab treatment to specified nuclides
+          do j = 1, list_iso_lab % size()
+            do k = 1, n
+              if (names % data(k) == list_iso_lab % data(j)) then
+                mat % p0(k) = .true.
+              end if
+            end do
           end do
-        end do
+        end if
       end if
 
       ! Check to make sure either all atom percents or all weight percents are
diff --git a/src/material_header.F90 b/src/material_header.F90
index eda0b42302..a3c14f8cab 100644
--- a/src/material_header.F90
+++ b/src/material_header.F90
@@ -57,7 +57,8 @@ module material_header
     logical :: fissionable = .false.
     logical :: depletable = .false.
 
-    ! enforce isotropic scattering in lab
+    ! enforce isotropic scattering in lab for specific nuclides
+    logical :: has_isotropic_nuclides = .false.
     logical, allocatable :: p0(:)
 
   contains
@@ -302,7 +303,6 @@ contains
     real(8) :: awr
     integer, allocatable :: new_nuclide(:)
     real(8), allocatable :: new_density(:)
-    logical, allocatable :: new_p0(:)
     character(:), allocatable :: name_
 
     name_ = to_f_string(name)
@@ -339,11 +339,6 @@ contains
             if (n > 0) new_density(1:n) = m % atom_density
             call move_alloc(FROM=new_density, TO=m % atom_density)
 
-            allocate(new_p0(n + 1))
-            if (n > 0) new_p0(1:n) = m % p0
-            new_p0(n + 1) = .false.
-            call move_alloc(FROM=new_p0, TO=m % p0)
-
             ! Append new nuclide/density
             k = nuclide_dict % get(to_lower(name_))
             m % nuclide(n + 1) = k
diff --git a/src/physics.F90 b/src/physics.F90
index cb309f93ac..fd6a0087c9 100644
--- a/src/physics.F90
+++ b/src/physics.F90
@@ -419,19 +419,22 @@ contains
     ! Set event component
     p % event = EVENT_SCATTER
 
-    ! Sample new outgoing angle for isotropic in lab scattering
-    if (materials(p % material) % p0(i_nuc_mat)) then
+    ! Sample new outgoing angle for isotropic-in-lab scattering
+    associate (mat => materials(p % material))
+      if (mat % has_isotropic_nuclides) then
+        if (materials(p % material) % p0(i_nuc_mat)) then
+          ! Sample isotropic-in-lab outgoing direction
+          uvw_new(1) = TWO * prn() - ONE
+          phi = TWO * PI * prn()
+          uvw_new(2) = cos(phi) * sqrt(ONE - uvw_new(1)*uvw_new(1))
+          uvw_new(3) = sin(phi) * sqrt(ONE - uvw_new(1)*uvw_new(1))
+          p % mu = dot_product(uvw_old, uvw_new)
 
-      ! Sample isotropic-in-lab outgoing direction
-      uvw_new(1) = TWO * prn() - ONE
-      phi = TWO * PI * prn()
-      uvw_new(2) = cos(phi) * sqrt(ONE - uvw_new(1)*uvw_new(1))
-      uvw_new(3) = sin(phi) * sqrt(ONE - uvw_new(1)*uvw_new(1))
-      p % mu = dot_product(uvw_old, uvw_new)
-
-      ! Change direction of particle
-      p % coord(1) % uvw = uvw_new
-    end if
+          ! Change direction of particle
+          p % coord(1) % uvw = uvw_new
+        end if
+      end if
+    end associate
 
   end subroutine scatter