diff --git a/src/libslic3r/SLA/SLABoilerPlate.hpp b/src/libslic3r/SLA/SLABoilerPlate.hpp
index 1436be17f..c1096206a 100644
--- a/src/libslic3r/SLA/SLABoilerPlate.hpp
+++ b/src/libslic3r/SLA/SLABoilerPlate.hpp
@@ -5,8 +5,8 @@
 #include <functional>
 #include <numeric>
 
-#include "ExPolygon.hpp"
-#include "TriangleMesh.hpp"
+#include <libslic3r/ExPolygon.hpp>
+#include <libslic3r/TriangleMesh.hpp>
 
 namespace Slic3r {
 namespace sla {
@@ -53,7 +53,7 @@ struct Contour3D {
 
     void merge(const Contour3D& ctr) {
         auto s3 = coord_t(points.size());
-        auto s = coord_t(indices.size());
+        auto s = indices.size();
 
         points.insert(points.end(), ctr.points.begin(), ctr.points.end());
         indices.insert(indices.end(), ctr.indices.begin(), ctr.indices.end());
@@ -62,6 +62,17 @@ struct Contour3D {
             auto& idx = indices[n]; x(idx) += s3; y(idx) += s3; z(idx) += s3;
         }
     }
+
+    // Write the index triangle structure to OBJ file for debugging purposes.
+    void to_obj(std::ostream& stream) {
+        for(auto& p : points) {
+            stream << "v " << p.transpose() << "\n";
+        }
+
+        for(auto& f : indices) {
+            stream << "f " << (f + Vec3i(1, 1, 1)).transpose() << "\n";
+        }
+    }
 };
 
 //using PointSet = Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic, Eigen::DontAlign>; //Eigen::MatrixXd;
diff --git a/src/libslic3r/SLA/SLASupportTree.cpp b/src/libslic3r/SLA/SLASupportTree.cpp
index 1d7858ead..b7ae95fda 100644
--- a/src/libslic3r/SLA/SLASupportTree.cpp
+++ b/src/libslic3r/SLA/SLASupportTree.cpp
@@ -9,8 +9,8 @@
 #include "SLASpatIndex.hpp"
 #include "SLABasePool.hpp"
 
-#include "ClipperUtils.hpp"
-#include "Model.hpp"
+#include <libslic3r/ClipperUtils.hpp>
+#include <libslic3r/Model.hpp>
 
 #include <boost/log/trivial.hpp>
 
@@ -176,6 +176,7 @@ Contour3D cylinder(double r, double h, size_t ssteps) {
     Vec3d jp = {0, 0, 0};
     Vec3d endp = {0, 0, h};
 
+    // Upper circle points
     for(int i = 0; i < steps; ++i) {
         double phi = i*a;
         double ex = endp(X) + r*std::cos(phi);
@@ -183,6 +184,7 @@ Contour3D cylinder(double r, double h, size_t ssteps) {
         points.emplace_back(ex, ey, endp(Z));
     }
 
+    // Lower circle points
     for(int i = 0; i < steps; ++i) {
         double phi = i*a;
         double x = jp(X) + r*std::cos(phi);
@@ -190,6 +192,7 @@ Contour3D cylinder(double r, double h, size_t ssteps) {
         points.emplace_back(x, y, jp(Z));
     }
 
+    // Now create long triangles connecting upper and lower circles
     indices.reserve(2*ssteps);
     auto offs = steps;
     for(int i = 0; i < steps - 1; ++i) {
@@ -197,10 +200,26 @@ Contour3D cylinder(double r, double h, size_t ssteps) {
         indices.emplace_back(i, offs + i + 1, i + 1);
     }
 
+    // Last triangle connecting the first and last vertices
     auto last = steps - 1;
     indices.emplace_back(0, last, offs);
     indices.emplace_back(last, offs + last, offs);
 
+    // According to the slicing algorithms, we need to aid them with generating
+    // a watertight body. So we create a triangle fan for the upper and lower
+    // ending of the cylinder to close the geometry.
+    points.emplace_back(jp); size_t ci = points.size() - 1;
+    for(int i = 0; i < steps - 1; ++i)
+        indices.emplace_back(i + offs + 1, i + offs, ci);
+
+    indices.emplace_back(offs, steps + offs - 1, ci);
+
+    points.emplace_back(endp); ci = points.size() - 1;
+    for(int i = 0; i < steps - 1; ++i)
+        indices.emplace_back(ci, i, i + 1);
+
+    indices.emplace_back(steps - 1, 0, ci);
+
     return ret;
 }
 
@@ -352,6 +371,8 @@ struct Pillar {
         r(radius), steps(st), endpoint(endp), starts_from_head(false)
     {
         assert(steps > 0);
+        assert(jp(Z) > endp(Z));    // Endpoint is below the starting point
+
         int steps_1 = int(steps - 1);
 
         auto& points = mesh.points;
@@ -382,6 +403,22 @@ struct Pillar {
 
         indices.emplace_back(0, steps_1, offs);
         indices.emplace_back(steps_1, offs + steps_1, offs);
+
+        // According to the slicing algorithms, we need to aid them with
+        // generating a watertight body. So we create a triangle fan for the
+        // upper and lower ending of the cylinder to close the geometry.
+        points.emplace_back(jp); size_t ci = points.size() - 1;
+        int stepsi = int(steps);
+        for(int i = 0; i < stepsi - 1; ++i)
+            indices.emplace_back(ci, i, i + 1);
+
+        indices.emplace_back(stepsi - 1, 0, ci);
+
+        points.emplace_back(endp); ci = points.size() - 1;
+        for(int i = 0; i < stepsi - 1; ++i)
+            indices.emplace_back(i + offs + 1, i + offs, ci);
+
+        indices.emplace_back(offs, stepsi + offs - 1, ci);
     }
 
     Pillar(const Junction& junc, const Vec3d& endp):
@@ -461,6 +498,8 @@ struct Bridge {
         Vec3d dir = (j2 - j1).normalized();
         double d = distance(j2, j1);
 
+        assert(d > 0);
+
         mesh = cylinder(r, d, steps);
 
         auto quater = Quaternion::FromTwoVectors(Vec3d{0,0,1}, dir);