diff --git a/src/plot.cpp b/src/plot.cpp
index 73dd43533..f3262185e 100644
--- a/src/plot.cpp
+++ b/src/plot.cpp
@@ -1100,7 +1100,7 @@ int ProjectionPlot::advance_to_boundary_from_void(Particle& p)
   else { // advance the particle
     for (int j = 0; j < p.n_coord(); ++j)
       p.coord(j).r += (min_dist + scoot) * p.coord(j).u;
-    return intersected_surface;
+    return std::abs(intersected_surface);
   }
 }
 
@@ -1321,7 +1321,7 @@ void ProjectionPlot::create_output() const
               this_line_segments[tid][horiz].emplace_back(
                 color_by_ == PlotColorBy::mats ? p.material()
                                                : p.coord(p.n_coord() - 1).cell,
-                dist.distance, dist.surface_index);
+                dist.distance, std::abs(dist.surface_index));
 
               // Advance particle
               for (int lev = 0; lev < p.n_coord(); ++lev) {
diff --git a/tests/regression_tests/plot_projections/plots.xml b/tests/regression_tests/plot_projections/plots.xml
index 11fa27211..85689da14 100644
--- a/tests/regression_tests/plot_projections/plots.xml
+++ b/tests/regression_tests/plot_projections/plots.xml
@@ -28,6 +28,7 @@
     <pixels>200 200</pixels>
     <background>240 240 240</background>
     <filename>example2.png</filename>
+    <wireframe_ids>2</wireframe_ids>
   </plot>
 
   <plot id="4" color_by="material" type="projection">
diff --git a/tests/regression_tests/plot_projections/results_true.dat b/tests/regression_tests/plot_projections/results_true.dat
index 7f41f6a40..f1f3d9276 100644
--- a/tests/regression_tests/plot_projections/results_true.dat
+++ b/tests/regression_tests/plot_projections/results_true.dat
@@ -1 +1 @@
-186d646c4959755bf809d35c9f33a931fbd5195145131ae6764955bf276d44acf24970dfff76001106b93a7ce239d67d569440136b13073082c8ee23419d721e
\ No newline at end of file
+18b85140df16cec9268e76d41430971be7f835b4ef84efdc0065012b2b341a6f369c14ad435a728d9224800882e4a923308859c5849cede0bc4b8ea4f3234f6f
\ No newline at end of file