diff --git a/src/libslic3r/Model.cpp b/src/libslic3r/Model.cpp
index e69929150..7893455da 100644
--- a/src/libslic3r/Model.cpp
+++ b/src/libslic3r/Model.cpp
@@ -963,7 +963,7 @@ void ModelObject::center_around_origin(bool include_modifiers)
 void ModelObject::ensure_on_bed(bool allow_negative_z)
 {
     const double min_z = get_min_z();
-    if (!allow_negative_z || min_z > 0.0)
+    if (!allow_negative_z || min_z > SINKING_Z_THRESHOLD)
         translate_instances({ 0.0, 0.0, -min_z });
 }
 #else
diff --git a/src/libslic3r/Model.hpp b/src/libslic3r/Model.hpp
index 0f64d2c98..1d4de4783 100644
--- a/src/libslic3r/Model.hpp
+++ b/src/libslic3r/Model.hpp
@@ -1129,6 +1129,10 @@ void check_model_ids_validity(const Model &model);
 void check_model_ids_equal(const Model &model1, const Model &model2);
 #endif /* NDEBUG */
 
+#if ENABLE_ALLOW_NEGATIVE_Z
+static const float SINKING_Z_THRESHOLD = -0.001f;
+#endif // ENABLE_ALLOW_NEGATIVE_Z
+
 } // namespace Slic3r
 
 namespace cereal
diff --git a/src/slic3r/GUI/3DScene.cpp b/src/slic3r/GUI/3DScene.cpp
index a32f8bb43..61b7e34fc 100644
--- a/src/slic3r/GUI/3DScene.cpp
+++ b/src/slic3r/GUI/3DScene.cpp
@@ -536,7 +536,7 @@ bool GLVolume::is_sinking() const
 #endif // DISABLE_ALLOW_NEGATIVE_Z_FOR_SLA
         return false;
     const BoundingBoxf3& box = transformed_convex_hull_bounding_box();
-    return box.min(2) < -EPSILON && box.max(2) >= -EPSILON;
+    return box.min.z() < SINKING_Z_THRESHOLD && box.max.z() >= SINKING_Z_THRESHOLD;
 }
 
 bool GLVolume::is_below_printbed() const
diff --git a/src/slic3r/GUI/GLCanvas3D.cpp b/src/slic3r/GUI/GLCanvas3D.cpp
index e8e4caed9..daf8c5991 100644
--- a/src/slic3r/GUI/GLCanvas3D.cpp
+++ b/src/slic3r/GUI/GLCanvas3D.cpp
@@ -3413,7 +3413,7 @@ void GLCanvas3D::do_move(const std::string& snapshot_type)
 #if ENABLE_ALLOW_NEGATIVE_Z
         const double shift_z = m->get_instance_min_z(i.second);
 #if DISABLE_ALLOW_NEGATIVE_Z_FOR_SLA
-        if (current_printer_technology() == ptSLA || shift_z > 0.0) {
+        if (current_printer_technology() == ptSLA || shift_z > SINKING_Z_THRESHOLD) {
 #else
         if (shift_z > 0.0) {
 #endif // DISABLE_ALLOW_NEGATIVE_Z_FOR_SLA
@@ -3463,7 +3463,7 @@ void GLCanvas3D::do_rotate(const std::string& snapshot_type)
         for (int i = 0; i < static_cast<int>(m_model->objects.size()); ++i) {
             const ModelObject* obj = m_model->objects[i];
             for (int j = 0; j < static_cast<int>(obj->instances.size()); ++j) {
-                min_zs[{ i, j }] = obj->instance_bounding_box(j).min(2);
+                min_zs[{ i, j }] = obj->instance_bounding_box(j).min.z();
             }
         }
     }
@@ -3508,7 +3508,7 @@ void GLCanvas3D::do_rotate(const std::string& snapshot_type)
 #if ENABLE_ALLOW_NEGATIVE_Z
         double shift_z = m->get_instance_min_z(i.second);
         // leave sinking instances as sinking
-        if (min_zs.empty() || min_zs.find({ i.first, i.second })->second >= 0.0 || shift_z > 0.0) {
+        if (min_zs.empty() || min_zs.find({ i.first, i.second })->second >= SINKING_Z_THRESHOLD || shift_z > SINKING_Z_THRESHOLD) {
             Vec3d shift(0.0, 0.0, -shift_z);
 #else
         Vec3d shift(0.0, 0.0, -m->get_instance_min_z(i.second));
@@ -3541,7 +3541,7 @@ void GLCanvas3D::do_scale(const std::string& snapshot_type)
         for (int i = 0; i < static_cast<int>(m_model->objects.size()); ++i) {
             const ModelObject* obj = m_model->objects[i];
             for (int j = 0; j < static_cast<int>(obj->instances.size()); ++j) {
-                min_zs[{ i, j }] = obj->instance_bounding_box(j).min(2);
+                min_zs[{ i, j }] = obj->instance_bounding_box(j).min.z();
             }
         }
     }
@@ -3583,7 +3583,7 @@ void GLCanvas3D::do_scale(const std::string& snapshot_type)
 #if ENABLE_ALLOW_NEGATIVE_Z
         double shift_z = m->get_instance_min_z(i.second);
         // leave sinking instances as sinking
-        if (min_zs.empty() || min_zs.find({ i.first, i.second })->second >= 0.0 || shift_z > 0.0) {
+        if (min_zs.empty() || min_zs.find({ i.first, i.second })->second >= SINKING_Z_THRESHOLD || shift_z > SINKING_Z_THRESHOLD) {
             Vec3d shift(0.0, 0.0, -shift_z);
 #else
         Vec3d shift(0.0, 0.0, -m->get_instance_min_z(i.second));
diff --git a/src/slic3r/GUI/GUI_ObjectManipulation.cpp b/src/slic3r/GUI/GUI_ObjectManipulation.cpp
index cdffbc88d..701a6daa9 100644
--- a/src/slic3r/GUI/GUI_ObjectManipulation.cpp
+++ b/src/slic3r/GUI/GUI_ObjectManipulation.cpp
@@ -360,7 +360,7 @@ ObjectManipulation::ObjectManipulation(wxWindow* parent) :
             if (0 <= idx && idx < static_cast<int>(objects.size())) {
                 const ModelObject* mo = wxGetApp().model().objects[idx];
                 const double min_z = mo->bounding_box().min.z();
-                if (std::abs(min_z) > EPSILON) {
+                if (std::abs(min_z) > SINKING_Z_THRESHOLD) {
                     Plater::TakeSnapshot snapshot(wxGetApp().plater(), _L("Drop to bed"));
                     change_position_value(2, m_cache.position.z() - min_z);
                 }
@@ -702,7 +702,11 @@ void ObjectManipulation::update_reset_buttons_visibility()
         }
         show_rotation = !rotation.isApprox(Vec3d::Zero());
         show_scale = !scale.isApprox(Vec3d::Ones());
+#if ENABLE_ALLOW_NEGATIVE_Z
+        show_drop_to_bed = std::abs(min_z) > SINKING_Z_THRESHOLD;
+#else
         show_drop_to_bed = (std::abs(min_z) > EPSILON);
+#endif // ENABLE_ALLOW_NEGATIVE_Z
     }
 
     wxGetApp().CallAfter([this, show_rotation, show_scale, show_drop_to_bed] {
diff --git a/src/slic3r/GUI/Plater.cpp b/src/slic3r/GUI/Plater.cpp
index ca87e244b..2e07d75c1 100644
--- a/src/slic3r/GUI/Plater.cpp
+++ b/src/slic3r/GUI/Plater.cpp
@@ -3247,7 +3247,7 @@ void Plater::priv::reload_from_disk()
             ModelVolume* old_volume = old_model_object->volumes[sel_v.volume_idx];
 
 #if ENABLE_ALLOW_NEGATIVE_Z
-            bool sinking = old_model_object->bounding_box().min.z() < 0.0;
+            bool sinking = old_model_object->bounding_box().min.z() < SINKING_Z_THRESHOLD;
 #endif // ENABLE_ALLOW_NEGATIVE_Z
 
             bool has_source = !old_volume->source.input_file.empty() && boost::algorithm::iequals(fs::path(old_volume->source.input_file).filename().string(), fs::path(path).filename().string());
@@ -4101,7 +4101,7 @@ bool Plater::priv::layers_height_allowed() const
 
     int obj_idx = get_selected_object_idx();
 #if ENABLE_ALLOW_NEGATIVE_Z
-    return 0 <= obj_idx && obj_idx < (int)model.objects.size() && model.objects[obj_idx]->bounding_box().max.z() > 0.0 &&
+    return 0 <= obj_idx && obj_idx < (int)model.objects.size() && model.objects[obj_idx]->bounding_box().max.z() > SINKING_Z_THRESHOLD &&
         config->opt_bool("variable_layer_height") && view3D->is_layers_editing_allowed();
 #else
     return 0 <= obj_idx && obj_idx < (int)model.objects.size() && config->opt_bool("variable_layer_height") && view3D->is_layers_editing_allowed();
@@ -6051,7 +6051,7 @@ void Plater::changed_objects(const std::vector<size_t>& object_idxs)
     for (size_t obj_idx : object_idxs) {
 #if ENABLE_ALLOW_NEGATIVE_Z
         if (obj_idx < p->model.objects.size()) {
-            if (p->model.objects[obj_idx]->bounding_box().min.z() >= 0.0)
+            if (p->model.objects[obj_idx]->bounding_box().min.z() >= SINKING_Z_THRESHOLD)
                 // re - align to Z = 0
                 p->model.objects[obj_idx]->ensure_on_bed();
         }