diff --git a/src/surface_header.F90 b/src/surface_header.F90
index 402e028ea1..8941fed725 100644
--- a/src/surface_header.F90
+++ b/src/surface_header.F90
@@ -1,6 +1,6 @@
 module surface_header
 
-  use constants, only: ONE, TWO, ZERO, INFINITY, FP_COINCIDENT, TINY_BIT
+  use constants, only: ONE, TWO, ZERO, INFINITY, FP_COINCIDENT
 
   implicit none
 
@@ -178,12 +178,13 @@ contains
 !===============================================================================
 ! SENSE determines whether a point is on the 'positive' or 'negative' side of a
 ! surface. This routine is crucial for determining what cell a particular point
-! is in.
+! is in. The positive side is indicated by a returned value of .true. and the
+! negative side is indicated by a returned value of .false.
 !===============================================================================
 
-  recursive function sense(this, xyz, uvw) result(s)
+  pure function sense(this, xyz, uvw) result(s)
     class(Surface), intent(in) :: this  ! surface
-    real(8), intent(inout) :: xyz(3)
+    real(8), intent(in) :: xyz(3)
     real(8), intent(in) :: uvw(3)
     logical :: s  ! sense of particle
 
@@ -195,16 +196,13 @@ contains
 
     ! Check which side of surface the point is on
     if (abs(f) < FP_COINCIDENT) then
-      ! Particle may be coincident with this surface. Artifically move the
-      ! particle forward a tiny bit.
-      xyz(:) = xyz + TINY_BIT * uvw
-      s = this%sense(xyz, uvw)
-    elseif (f > 0) then
-      s = .true.
+      ! Particle may be coincident with this surface. To determine the sense, we
+      ! look at the direction of the particle relative to the surface normal (by
+      ! default in the positive direction) via their dot product.
+      s = (dot_product(uvw, this%normal(xyz)) > ZERO)
     else
-      s = .false.
+      s = (f > ZERO)
     end if
-
   end function sense
 
   subroutine reflect(this, xyz, uvw)
diff --git a/tests/test_plot_basis/results_true.dat b/tests/test_plot_basis/results_true.dat
index ae588fd4f3..b1d5dc8534 100644
--- a/tests/test_plot_basis/results_true.dat
+++ b/tests/test_plot_basis/results_true.dat
@@ -1 +1 @@
-6a2400a95ea5baee432dd04a85252818d682004dc80b225b99c4bbc7cfd20d8523bd8e5df8a272df288cb2f300e5eee55f7ffa7b4d28ea64f92b78839ab0e86b
\ No newline at end of file
+368e0135c136d5c8a2dabb4c8085279dc7ac0bd81b2ec905bdf11ecb5fe99803868631cdff0b3ddec941323bcc661747d4c16edfd4f8d38582155bd6fd7e82e8
\ No newline at end of file
diff --git a/tests/test_plot_mask/results_true.dat b/tests/test_plot_mask/results_true.dat
index 1076324545..a1e323203d 100644
--- a/tests/test_plot_mask/results_true.dat
+++ b/tests/test_plot_mask/results_true.dat
@@ -1 +1 @@
-d888a734d6e69c5ca92457dc865c4defd8a1d8a1d4a01e0c8e7c528dde25d96df1283da37889dac0857329051958be2f2b491f2fd2bc22c8424a60ec6cda04bd
\ No newline at end of file
+a7cb65bf40c84c0540d45ff292c398f9ae51b3d9396e88b9b4e5cdf05e8730f409bddb53aec6d396058194c6293c5bd3ef39efd0b0f30f2423f696193c85176c
\ No newline at end of file