diff --git a/lib/Slic3r/GUI/PreviewCanvas.pm b/lib/Slic3r/GUI/PreviewCanvas.pm
index 436854d36..ada211705 100644
--- a/lib/Slic3r/GUI/PreviewCanvas.pm
+++ b/lib/Slic3r/GUI/PreviewCanvas.pm
@@ -407,7 +407,7 @@ sub SetCuttingPlane {
     my @verts = ();
     foreach my $volume (@{$self->volumes}) {
         foreach my $volume (@{$self->volumes}) {
-            my $expolygons = $volume->mesh->slice([ $z + $volume->origin->z ])->[0];
+            my $expolygons = $volume->mesh->slice([ $z - $volume->origin->z ])->[0];
             $expolygons = offset_ex([ map @$_, @$expolygons ], scale 0.1);
             
             foreach my $line (map @{$_->lines}, map @$_, @$expolygons) {