diff --git a/xs/src/TriangleMesh.cpp b/xs/src/TriangleMesh.cpp
index dcdf7580..58a4a588 100644
--- a/xs/src/TriangleMesh.cpp
+++ b/xs/src/TriangleMesh.cpp
@@ -270,13 +270,6 @@ TriangleMesh::slice(const std::vector<float> &z, std::vector<Polygons>* layers)
         printf("z: min = %.2f, max = %.2f\n", min_z, max_z);
         #endif
         
-        if (min_z == max_z) {
-            #ifdef SLIC3R_DEBUG
-            printf("Facet is horizontal; ignoring\n");
-            #endif
-            continue;
-        }
-        
         // find layer extents
         std::vector<float>::const_iterator min_layer, max_layer;
         min_layer = std::lower_bound(z.begin(), z.end(), min_z); // first layer whose slice_z is >= min_z
@@ -319,7 +312,9 @@ TriangleMesh::slice(const std::vector<float> &z, std::vector<Polygons>* layers)
                     stl_vertex* v1 = &v_scaled_shared[ this->stl.v_indices[facet_idx].vertex[1] ];
                     stl_vertex* v2 = &v_scaled_shared[ this->stl.v_indices[facet_idx].vertex[2] ];
                     IntersectionLine line;
-                    if (v0->z < slice_z || v1->z < slice_z || v2->z < slice_z) {
+                    if (min_z == max_z) {
+                        line.edge_type = feHorizontal;
+                    } else if (v0->z < slice_z || v1->z < slice_z || v2->z < slice_z) {
                         line.edge_type = feTop;
                         std::swap(a, b);
                         std::swap(a_id, b_id);
@@ -335,7 +330,10 @@ TriangleMesh::slice(const std::vector<float> &z, std::vector<Polygons>* layers)
                     
                     lines[layer_idx].push_back(line);
                     found_horizontal_edge = true;
-                    break;
+                    
+                    // if this is a top or bottom edge, we can stop looping through edges
+                    // because we won't find anything interesting
+                    if (line.edge_type != feHorizontal) break;
                 } else if (a->z == slice_z) {
                     IntersectionPoint point;
                     point.x         = a->x;
@@ -398,6 +396,13 @@ TriangleMesh::slice(const std::vector<float> &z, std::vector<Polygons>* layers)
         printf("Layer %d:\n", layer_idx);
         #endif
         
+        /*
+        SVG svg("lines.svg");
+        for (IntersectionLines::iterator line = it->begin(); line != it->end(); ++line)
+            svg.AddLine(*line);
+        svg.Close();
+        */
+        
         // remove tangent edges
         for (IntersectionLines::iterator line = it->begin(); line != it->end(); ++line) {
             if (line->skip || line->edge_type == feNone) continue;
@@ -421,6 +426,13 @@ TriangleMesh::slice(const std::vector<float> &z, std::vector<Polygons>* layers)
                         line->skip = true;
                         break;
                     }
+                } else if (line->a_id == line2->b_id && line->b_id == line2->a_id) {
+                    /* if this edge joins two horizontal facets, remove both of them */
+                    if (line->edge_type == feHorizontal && line2->edge_type == feHorizontal) {
+                        line->skip = true;
+                        line2->skip = true;
+                        break;
+                    }
                 }
             }
         }
diff --git a/xs/src/TriangleMesh.hpp b/xs/src/TriangleMesh.hpp
index f20340b4..7efb0945 100644
--- a/xs/src/TriangleMesh.hpp
+++ b/xs/src/TriangleMesh.hpp
@@ -49,7 +49,7 @@ class TriangleMesh
     void require_shared_vertices();
 };
 
-enum FacetEdgeType { feNone, feTop, feBottom };
+enum FacetEdgeType { feNone, feTop, feBottom, feHorizontal };
 
 class IntersectionPoint : public Point
 {