diff --git a/src/libslic3r/SLA/Hollowing.cpp b/src/libslic3r/SLA/Hollowing.cpp
index 6329172669..b387845215 100644
--- a/src/libslic3r/SLA/Hollowing.cpp
+++ b/src/libslic3r/SLA/Hollowing.cpp
@@ -421,7 +421,8 @@ void divide_triangle(const DivFace &face, Fn &&visitor)
         divide_triangle(child2, std::forward<Fn>(visitor));
 }
 
-void remove_inside_triangles(TriangleMesh &mesh, const Interior &interior)
+void remove_inside_triangles(TriangleMesh &mesh, const Interior &interior,
+                             const std::vector<bool> &exclude_mask)
 {
     enum TrPos { posInside, posTouch, posOutside };
 
@@ -429,6 +430,11 @@ void remove_inside_triangles(TriangleMesh &mesh, const Interior &interior)
     auto &vertices    = mesh.its.vertices;
     auto bb           = mesh.bounding_box();
 
+    bool use_exclude_mask = faces.size() == exclude_mask.size();
+    auto is_excluded = [&exclude_mask, use_exclude_mask](size_t face_id) {
+        return use_exclude_mask && exclude_mask[face_id];
+    };
+
     // TODO: Parallel mode not working yet
     using exec_policy = ccr_seq;
 
@@ -518,6 +524,10 @@ void remove_inside_triangles(TriangleMesh &mesh, const Interior &interior)
     exec_policy::for_each(size_t(0), faces.size(), [&] (size_t face_idx) {
         const Vec3i &face = faces[face_idx];
 
+        // If the triangle is excluded, we need to keep it.
+        if (is_excluded(face_idx))
+            return;
+
         std::array<Vec3f, 3> pts =
             { vertices[face(0)], vertices[face(1)], vertices[face(2)] };
 
diff --git a/src/libslic3r/SLA/Hollowing.hpp b/src/libslic3r/SLA/Hollowing.hpp
index caa7d7b6ba..5d2181e7a6 100644
--- a/src/libslic3r/SLA/Hollowing.hpp
+++ b/src/libslic3r/SLA/Hollowing.hpp
@@ -81,7 +81,16 @@ void hollow_mesh(TriangleMesh &mesh, const HollowingConfig &cfg, int flags = 0);
 // Hollowing prepared in "interior", merge with original mesh
 void hollow_mesh(TriangleMesh &mesh, const Interior &interior, int flags = 0);
 
-void remove_inside_triangles(TriangleMesh &mesh, const Interior &interior);
+void remove_inside_triangles(TriangleMesh &mesh, const Interior &interior,
+                             const std::vector<bool> &exclude_mask = {});
+
+double get_distance(const Vec3f &p, const Interior &interior);
+
+template<class T>
+FloatingOnly<T> get_distance(const Vec<3, T> &p, const Interior &interior)
+{
+    return get_distance(Vec3f(p.template cast<float>()), interior);
+}
 
 void cut_drainholes(std::vector<ExPolygons> & obj_slices,
                     const std::vector<float> &slicegrid,
diff --git a/src/libslic3r/SLAPrintSteps.cpp b/src/libslic3r/SLAPrintSteps.cpp
index fe5d7505f9..455141051b 100644
--- a/src/libslic3r/SLAPrintSteps.cpp
+++ b/src/libslic3r/SLAPrintSteps.cpp
@@ -1,3 +1,5 @@
+#include <unordered_set>
+
 #include <libslic3r/Exception.hpp>
 #include <libslic3r/SLAPrintSteps.hpp>
 #include <libslic3r/MeshBoolean.hpp>
@@ -142,6 +144,136 @@ void SLAPrint::Steps::hollow_model(SLAPrintObject &po)
     }
 }
 
+
+struct FaceHash {
+
+    // A hash is created for each triangle to be identifiable. The hash uses
+    // only the triangle's geometric traits, not the index in a particular mesh.
+    std::unordered_set<std::string> facehash;
+
+    static std::string facekey(const Vec3i &face,
+                               const std::vector<Vec3f> &vertices)
+    {
+        // Scale to integer to avoid floating points
+        std::array<Vec<3, int64_t>, 3> pts = {
+            scaled<int64_t>(vertices[face(0)]),
+            scaled<int64_t>(vertices[face(1)]),
+            scaled<int64_t>(vertices[face(2)])
+        };
+
+        // Get the first two sides of the triangle, do a cross product and move
+        // that vector to the center of the triangle. This encodes all
+        // information to identify an identical triangle at the same position.
+        Vec<3, int64_t> a = pts[0] - pts[2], b = pts[1] - pts[2];
+        Vec<3, int64_t> c = a.cross(b) + (pts[0] + pts[1] + pts[2]) / 3;
+
+        // Return a concatenated string representation of the coordinates
+        return std::to_string(c(0)) + std::to_string(c(1)) + std::to_string(c(2));
+    };
+
+    FaceHash(const indexed_triangle_set &its)
+    {
+        for (const Vec3i &face : its.indices) {
+            std::string keystr = facekey(face, its.vertices);
+            facehash.insert(keystr);
+        }
+    }
+
+    bool find(const std::string &key)
+    {
+        auto it = facehash.find(key);
+        return it != facehash.end();
+    }
+};
+
+// Create exclude mask for triangle removal inside hollowed interiors.
+// This is necessary when the interior is already part of the mesh which was
+// drilled using CGAL mesh boolean operation. Excluded will be the triangles
+// originally part of the interior mesh and triangles that make up the drilled
+// hole walls.
+static std::vector<bool> create_exclude_mask(
+        const indexed_triangle_set &its,
+        const sla::Interior &interior,
+        const std::vector<sla::DrainHole> &holes)
+{
+    FaceHash interior_hash{sla::get_mesh(interior).its};
+
+    std::vector<bool> exclude_mask(its.indices.size(), false);
+
+    std::vector< std::vector<size_t> > neighbor_index =
+            create_neighbor_index(its);
+
+    auto exclude_neighbors = [&neighbor_index, &exclude_mask](const Vec3i &face)
+    {
+        for (int i = 0; i < 3; ++i) {
+            const std::vector<size_t> &neighbors = neighbor_index[face(i)];
+            for (size_t fi_n : neighbors) exclude_mask[fi_n] = true;
+        }
+    };
+
+    for (size_t fi = 0; fi < its.indices.size(); ++fi) {
+        auto &face = its.indices[fi];
+
+        std::string key =
+                FaceHash::facekey(face, its.vertices);
+
+        if (interior_hash.find(key)) {
+            exclude_mask[fi] = true;
+            continue;
+        }
+
+        if (exclude_mask[fi]) {
+            exclude_neighbors(face);
+            continue;
+        }
+
+        // Lets deal with the holes. All the triangles of a hole and all the
+        // neighbors of these triangles need to be kept. The neigbors were
+        // created by CGAL mesh boolean operation that modified the original
+        // interior inside the input mesh to contain the holes.
+        Vec3d tr_center = (
+            its.vertices[face(0)] +
+            its.vertices[face(1)] +
+            its.vertices[face(2)]
+        ).cast<double>() / 3.;
+
+        // If the center is more than half a mm inside the interior,
+        // it cannot possibly be part of a hole wall.
+        if (sla::get_distance(tr_center, interior) < -0.5)
+            continue;
+
+        Vec3f U = its.vertices[face(1)] - its.vertices[face(0)];
+        Vec3f V = its.vertices[face(2)] - its.vertices[face(0)];
+        Vec3f C = U.cross(V);
+        Vec3f face_normal = C.normalized();
+
+        for (const sla::DrainHole &dh : holes) {
+            Vec3d dhpos = dh.pos.cast<double>();
+            Vec3d dhend = dhpos + dh.normal.cast<double>() * dh.height;
+
+            Linef3 holeaxis{dhpos, dhend};
+
+            double D_hole_center = line_alg::distance_to(holeaxis, tr_center);
+            double D_hole        = std::abs(D_hole_center - dh.radius);
+            float dot            = dh.normal.dot(face_normal);
+
+            // Empiric tolerances for center distance and normals angle.
+            // For triangles that are part of a hole wall the angle of
+            // triangle normal and the hole axis is around 90 degrees,
+            // so the dot product is around zero.
+            double D_tol = dh.radius / sla::DrainHole::steps;
+            float normal_angle_tol = 1.f / sla::DrainHole::steps;
+
+            if (D_hole < D_tol && std::abs(dot) < normal_angle_tol) {
+                exclude_mask[fi] = true;
+                exclude_neighbors(face);
+            }
+        }
+    }
+
+    return exclude_mask;
+}
+
 // Drill holes into the hollowed/original mesh.
 void SLAPrint::Steps::drill_holes(SLAPrintObject &po)
 {
@@ -207,10 +339,13 @@ void SLAPrint::Steps::drill_holes(SLAPrintObject &po)
         hollowed_mesh = MeshBoolean::cgal::cgal_to_triangle_mesh(*hollowed_mesh_cgal);
         mesh_view = hollowed_mesh;
 
-        if (is_hollowed)
-            sla::remove_inside_triangles(mesh_view,
-                                         *po.m_hollowing_data->interior,
-                                         drainholes);
+        if (is_hollowed) {
+            auto &interior = *po.m_hollowing_data->interior;
+            std::vector<bool> exclude_mask =
+                    create_exclude_mask(mesh_view.its, interior, drainholes);
+
+            sla::remove_inside_triangles(mesh_view, interior, exclude_mask);
+        }
 
     } catch (const std::runtime_error &) {
         throw Slic3r::SlicingError(L(
diff --git a/src/libslic3r/TriangleMesh.cpp b/src/libslic3r/TriangleMesh.cpp
index adb9be64d1..d5a3490877 100644
--- a/src/libslic3r/TriangleMesh.cpp
+++ b/src/libslic3r/TriangleMesh.cpp
@@ -2063,4 +2063,22 @@ TriangleMesh make_sphere(double radius, double fa)
 	return mesh;
 }
 
+std::vector<std::vector<size_t> > create_neighbor_index(const indexed_triangle_set &its)
+{
+    if (its.vertices.empty()) return {};
+
+    size_t res = its.indices.size() / its.vertices.size();
+    std::vector< std::vector<size_t> > index(its.vertices.size(),
+                                             reserve_vector<size_t>(res));
+
+    for (size_t fi = 0; fi < its.indices.size(); ++fi) {
+        auto &face = its.indices[fi];
+        index[face(0)].emplace_back(fi);
+        index[face(1)].emplace_back(fi);
+        index[face(2)].emplace_back(fi);
+    }
+
+    return index;
+}
+
 }
diff --git a/src/libslic3r/TriangleMesh.hpp b/src/libslic3r/TriangleMesh.hpp
index 9625298f4e..e6f6dc84b8 100644
--- a/src/libslic3r/TriangleMesh.hpp
+++ b/src/libslic3r/TriangleMesh.hpp
@@ -89,6 +89,12 @@ private:
     std::deque<uint32_t> find_unvisited_neighbors(std::vector<unsigned char> &facet_visited) const;
 };
 
+// Create an index of faces belonging to each vertex. The returned vector can
+// be indexed with vertex indices and contains a list of face indices for each
+// vertex.
+std::vector< std::vector<size_t> >
+create_neighbor_index(const indexed_triangle_set &its);
+
 enum FacetEdgeType { 
     // A general case, the cutting plane intersect a face at two different edges.
     feGeneral,