diff --git a/src/mesh.F90 b/src/mesh.F90
index 3e489903b4..37847d58ac 100644
--- a/src/mesh.F90
+++ b/src/mesh.F90
@@ -218,7 +218,9 @@ contains
   end subroutine count_fission_sites
 
 !===============================================================================
-! MESH_INTERSECT
+! MESH_INTERSECT determines if a line between xyz0 and xyz1 intersects the outer
+! boundary of the given mesh. This is important for determining whether a track
+! will score to a mesh tally.
 !===============================================================================
 
   function mesh_intersects(m, xyz0, xyz1) result(intersects)
@@ -228,9 +230,11 @@ contains
     real(8), intent(in) :: xyz1(3)
     logical :: intersects
 
-    real(8) :: x0, y0, z0 ! track start point
-    real(8) :: x1, y1, z1 ! track end point
-    real(8) :: xi, yi, zi ! track intersection point with mesh
+    real(8) :: x0, y0, z0    ! track start point
+    real(8) :: x1, y1, z1    ! track end point
+    real(8) :: xi, yi, zi    ! track intersection point with mesh
+    real(8) :: xm0, ym0, zm0 ! lower-left coordinates of mesh
+    real(8) :: xm1, ym1, zm1 ! upper-right coordinates of mesh
 
     ! Copy coordinates of starting point
     x0 = xyz0(1)
@@ -242,62 +246,66 @@ contains
     y1 = xyz1(2)
     z1 = xyz1(3)
 
+    ! Copy coordinates of mesh lower_left
+    xm0 = m % lower_left(1)
+    ym0 = m % lower_left(2)
+    zm0 = m % lower_left(3)
+
+    ! Copy coordinates of mesh upper_right
+    xm1 = m % upper_right(1)
+    ym1 = m % upper_right(2)
+    zm1 = m % upper_right(3)
+
     ! Check if line intersects bottom surface -- calculate the intersection
     ! point (y,z)
-    xi = m % lower_left(1)
-    yi = y0 + (xi - x0) * (y1 - y0) / (x1 - x0)
-    zi = z0 + (xi - x0) * (z1 - z0) / (x1 - x0)
-    if (yi >= y0 .and. yi < y1 .and. zi >= z0 .and. zi < z1) then
+    yi = y0 + (xm0 - x0) * (y1 - y0) / (x1 - x0)
+    zi = z0 + (xm0 - x0) * (z1 - z0) / (x1 - x0)
+    if (yi >= ym0 .and. yi < ym1 .and. zi >= zm0 .and. zi < zm1) then
        intersects = .true.
        return
     end if
     
     ! Check if line intersects left surface -- calculate the intersection point
     ! (x,z)
-    yi = m % lower_left(2)
-    xi = x0 + (yi - y0) * (x1 - x0) / (y1 - y0)
-    zi = z0 + (yi - y0) * (z1 - z0) / (y1 - y0)
-    if (xi >= x0 .and. xi < x1 .and. zi >= z0 .and. zi < z1) then
+    xi = x0 + (ym0 - y0) * (x1 - x0) / (y1 - y0)
+    zi = z0 + (ym0 - y0) * (z1 - z0) / (y1 - y0)
+    if (xi >= xm0 .and. xi < xm1 .and. zi >= zm0 .and. zi < zm1) then
        intersects = .true.
        return
     end if
     
     ! Check if line intersects front surface -- calculate the intersection point
     ! (x,y)
-    zi = m % lower_left(3)
-    xi = x0 + (zi - z0) * (x1 - x0) / (z1 - z0)
-    yi = y0 + (zi - z0) * (y1 - y0) / (z1 - z0)
-    if (xi >= x0 .and. xi < x1 .and. yi >= y0 .and. yi < y1) then
+    xi = x0 + (zm0 - z0) * (x1 - x0) / (z1 - z0)
+    yi = y0 + (zm0 - z0) * (y1 - y0) / (z1 - z0)
+    if (xi >= xm0 .and. xi < xm1 .and. yi >= ym0 .and. yi < ym1) then
        intersects = .true.
        return
     end if
     
     ! Check if line intersects top surface -- calculate the intersection
     ! point (y,z)
-    xi = m % upper_right(1)
-    yi = y0 + (xi - x0) * (y1 - y0) / (x1 - x0)
-    zi = z0 + (xi - x0) * (z1 - z0) / (x1 - x0)
-    if (yi >= y0 .and. yi < y1 .and. zi >= z0 .and. zi < z1) then
+    yi = y0 + (xm1 - x0) * (y1 - y0) / (x1 - x0)
+    zi = z0 + (xm1 - x0) * (z1 - z0) / (x1 - x0)
+    if (yi >= ym0 .and. yi < ym1 .and. zi >= zm0 .and. zi < zm1) then
        intersects = .true.
        return
     end if
     
     ! Check if line intersects right surface -- calculate the intersection point
     ! (x,z)
-    yi = m % upper_right(2)
-    xi = x0 + (yi - y0) * (x1 - x0) / (y1 - y0)
-    zi = z0 + (yi - y0) * (z1 - z0) / (y1 - y0)
-    if (xi >= x0 .and. xi < x1 .and. zi >= z0 .and. zi < z1) then
+    xi = x0 + (ym1 - y0) * (x1 - x0) / (y1 - y0)
+    zi = z0 + (ym1 - y0) * (z1 - z0) / (y1 - y0)
+    if (xi >= xm0 .and. xi < xm1 .and. zi >= zm0 .and. zi < zm1) then
        intersects = .true.
        return
     end if
     
     ! Check if line intersects back surface -- calculate the intersection point
     ! (x,y)
-    zi = m % upper_right(3)
-    xi = x0 + (zi - z0) * (x1 - x0) / (z1 - z0)
-    yi = y0 + (zi - z0) * (y1 - y0) / (z1 - z0)
-    if (xi >= x0 .and. xi < x1 .and. yi >= y0 .and. yi < y1) then
+    xi = x0 + (zm1 - z0) * (x1 - x0) / (z1 - z0)
+    yi = y0 + (zm1 - z0) * (y1 - y0) / (z1 - z0)
+    if (xi >= xm0 .and. xi < xm1 .and. yi >= ym0 .and. yi < ym1) then
        intersects = .true.
        return
     end if