diff --git a/src/libslic3r/Model.cpp b/src/libslic3r/Model.cpp
index 8eb5bb3890..e32285106e 100644
--- a/src/libslic3r/Model.cpp
+++ b/src/libslic3r/Model.cpp
@@ -959,7 +959,7 @@ void ModelObject::ensure_on_bed(bool allow_negative_z)
     double z_offset = 0.0;
 
     if (allow_negative_z) {
-        if (volumes.size() == 1)
+        if (parts_count() == 1)
             z_offset = -get_min_z();
         else {
             const double max_z = get_max_z();
@@ -1127,6 +1127,15 @@ size_t ModelObject::facets_count() const
     return num;
 }
 
+size_t ModelObject::parts_count() const
+{
+    size_t num = 0;
+    for (const ModelVolume* v : this->volumes)
+        if (v->is_model_part())
+            ++num;
+    return num;
+}
+
 bool ModelObject::needed_repair() const
 {
     for (const ModelVolume *v : this->volumes)
diff --git a/src/libslic3r/Model.hpp b/src/libslic3r/Model.hpp
index 25f19e7928..b89dd5aa1e 100644
--- a/src/libslic3r/Model.hpp
+++ b/src/libslic3r/Model.hpp
@@ -347,6 +347,7 @@ public:
 
     size_t materials_count() const;
     size_t facets_count() const;
+    size_t parts_count() const;
     bool needed_repair() const;
     ModelObjectPtrs cut(size_t instance, coordf_t z, ModelObjectCutAttributes attributes);
     void split(ModelObjectPtrs* new_objects);
diff --git a/src/slic3r/GUI/Selection.cpp b/src/slic3r/GUI/Selection.cpp
index ba4577bfb0..3409c531da 100644
--- a/src/slic3r/GUI/Selection.cpp
+++ b/src/slic3r/GUI/Selection.cpp
@@ -2154,11 +2154,23 @@ void Selection::ensure_not_below_bed()
         }
     }
 
-    for (GLVolume* volume : *m_volumes) {
-        std::pair<int, int> instance = std::make_pair(volume->object_idx(), volume->instance_idx());
-        InstancesToZMap::iterator it = instances_max_z.find(instance);
-        if (it != instances_max_z.end() && it->second < SINKING_MIN_Z_THRESHOLD)
-            volume->set_instance_offset(Z, volume->get_instance_offset(Z) + SINKING_MIN_Z_THRESHOLD - it->second);
+    if (is_any_volume()) {
+        for (unsigned int i : m_list) {
+            GLVolume& volume = *(*m_volumes)[i];
+            std::pair<int, int> instance = std::make_pair(volume.object_idx(), volume.instance_idx());
+            InstancesToZMap::iterator it = instances_max_z.find(instance);
+            double z_shift = SINKING_MIN_Z_THRESHOLD - it->second;
+            if (it != instances_max_z.end() && z_shift > 0.0)
+                volume.set_volume_offset(Z, volume.get_volume_offset(Z) + z_shift);
+        }
+    }
+    else {
+        for (GLVolume* volume : *m_volumes) {
+            std::pair<int, int> instance = std::make_pair(volume->object_idx(), volume->instance_idx());
+            InstancesToZMap::iterator it = instances_max_z.find(instance);
+            if (it != instances_max_z.end() && it->second < SINKING_MIN_Z_THRESHOLD)
+                volume->set_instance_offset(Z, volume->get_instance_offset(Z) + SINKING_MIN_Z_THRESHOLD - it->second);
+        }
     }
 }