diff --git a/lib/Slic3r/GUI/3DScene.pm b/lib/Slic3r/GUI/3DScene.pm
index 1ff174c5d1..740fbcc109 100644
--- a/lib/Slic3r/GUI/3DScene.pm
+++ b/lib/Slic3r/GUI/3DScene.pm
@@ -1653,7 +1653,7 @@ has 'layer_height_texture_cells'  => (is => 'rw');
 
 sub object_idx {
     my ($self) = @_;
-    return $self->composite_id / 1000000;
+    return int($self->composite_id / 1000000);
 }
 
 sub volume_idx {