diff --git a/lib/Slic3r/GCode/Layer.pm b/lib/Slic3r/GCode/Layer.pm
index df3e85b945..af296edf08 100644
--- a/lib/Slic3r/GCode/Layer.pm
+++ b/lib/Slic3r/GCode/Layer.pm
@@ -18,7 +18,7 @@ sub _build_spiralvase {
     my $self = shift;
     
     return $Slic3r::Config->spiral_vase
-        ? Slic3r::GCode::SpiralVase->new
+        ? Slic3r::GCode::SpiralVase->new(config => $self->gcodegen->config)
         : undef;
 }
 
diff --git a/lib/Slic3r/GCode/SpiralVase.pm b/lib/Slic3r/GCode/SpiralVase.pm
index 1c94b251a9..1094e728e2 100644
--- a/lib/Slic3r/GCode/SpiralVase.pm
+++ b/lib/Slic3r/GCode/SpiralVase.pm
@@ -1,6 +1,8 @@
 package Slic3r::GCode::SpiralVase;
 use Moo;
 
+has 'config' => (is => 'ro', required => 1);
+
 use Slic3r::Geometry qw(unscale);
 
 sub process_layer {
@@ -16,7 +18,7 @@ sub process_layer {
     
     my $new_gcode = "";
     my $layer_height = $layer->height;
-    my $z = $layer->print_z - $layer_height;
+    my $z = $layer->print_z + $self->config->z_offset - $layer_height;
     my $newlayer = 0;
     Slic3r::GCode::Reader->new(gcode => $gcode)->parse(sub {
         my ($reader, $cmd, $args, $info) = @_;
diff --git a/t/shells.t b/t/shells.t
index 8cfcc87f69..bd4b221c65 100644
--- a/t/shells.t
+++ b/t/shells.t
@@ -1,4 +1,4 @@
-use Test::More tests => 6;
+use Test::More tests => 10;
 use strict;
 use warnings;
 
@@ -104,6 +104,7 @@ use Slic3r::Test;
     $config->set('spiral_vase', 1);
     $config->set('bottom_solid_layers', 0);
     $config->set('skirts', 0);
+    $config->set('first_layer_height', '100%');
     
     # TODO: this needs to be tested with a model with sloping edges, where starting
     # points of each layer are not aligned - in that case we would test that no
@@ -114,18 +115,25 @@ use Slic3r::Test;
         my $print = Slic3r::Test::init_print($model_name, config => $config);
         my $travel_moves_after_first_extrusion = 0;
         my $started_extruding = 0;
+        my @z_steps = ();
         Slic3r::GCode::Reader->new(gcode => Slic3r::Test::gcode($print))->parse(sub {
             my ($self, $cmd, $args, $info) = @_;
             
             $started_extruding = 1 if $info->{extruding};
+            push @z_steps, ($args->{Z} - $self->Z)
+                if $started_extruding && exists $args->{Z};
             $travel_moves_after_first_extrusion++
                 if $info->{travel} && $started_extruding && !exists $args->{Z};
         });
         is $travel_moves_after_first_extrusion, 0, "no gaps in spiral vase ($description)";
+        ok !(grep { $_ > $config->layer_height } @z_steps), "no gaps in Z ($description)";
     };
     
     $test->('20mm_cube', 'solid model');
     $test->('40x10', 'hollow model');
+    
+    $config->set('z_offset', -10);
+    $test->('20mm_cube', 'solid model with negative z-offset');
 }
 
 __END__