diff --git a/lib/Slic3r/GCode/Layer.pm b/lib/Slic3r/GCode/Layer.pm
index 832e4f157..4f453d160 100644
--- a/lib/Slic3r/GCode/Layer.pm
+++ b/lib/Slic3r/GCode/Layer.pm
@@ -149,6 +149,8 @@ sub process_layer {
             my @perimeters_by_island = map [], 0..$#{$layer->slices};   # slice idx => @perimeters
             my @infill_by_island     = map [], 0..$#{$layer->slices};   # slice idx => @fills
             
+            # NOTE: we assume $layer->slices was already ordered with chained_path()!
+            
             PERIMETER: foreach my $perimeter (@{$layerm->perimeters}) {
                 for my $i (0 .. $#{$layer->slices}-1) {
                     if ($layer->slices->[$i]->contour->contains_point($perimeter->first_point)) {
diff --git a/lib/Slic3r/Layer.pm b/lib/Slic3r/Layer.pm
index f65c1d133..91961f602 100644
--- a/lib/Slic3r/Layer.pm
+++ b/lib/Slic3r/Layer.pm
@@ -2,7 +2,7 @@ package Slic3r::Layer;
 use Moo;
 
 use List::Util qw(first);
-use Slic3r::Geometry qw(scale);
+use Slic3r::Geometry qw(scale chained_path);
 use Slic3r::Geometry::Clipper qw(union_ex);
 
 has 'id'                => (is => 'rw', required => 1); # sequential number of layer, 0-based
@@ -44,6 +44,10 @@ sub make_slices {
     my $self = shift;
     
     my $slices = union_ex([ map $_->p, map @{$_->slices}, @{$self->regions} ]);
+    
+    # sort slices
+    $slices = [ @$slices[@{chained_path([ map $_->contour->first_point, @$slices ])}] ];
+    
     $self->slices->clear;
     $self->slices->append(@$slices);
 }
diff --git a/lib/Slic3r/Layer/Region.pm b/lib/Slic3r/Layer/Region.pm
index 4bc39e105..ce6fac54f 100644
--- a/lib/Slic3r/Layer/Region.pm
+++ b/lib/Slic3r/Layer/Region.pm
@@ -284,8 +284,16 @@ sub make_perimeters {
         
         # use a nearest neighbor search to order these children
         # TODO: supply second argument to chained_path() too?
-        my $sorted_collection = $collection->chained_path_indices(0);
-        my @orig_indices = @{$sorted_collection->orig_indices};
+        # Optimization: since islands are going to be sorted by slice anyway in the 
+        # G-code export process, we skip chained_path here
+        my ($sorted_collection, @orig_indices);
+        if ($is_contour && $depth == 0) {
+            $sorted_collection = $collection;
+            @orig_indices = (0..$#$sorted_collection);
+        } else {
+            $sorted_collection = $collection->chained_path_indices(0);
+            @orig_indices = @{$sorted_collection->orig_indices};
+        }
         
         my @loops = ();
         foreach my $loop (@$sorted_collection) {
diff --git a/xs/xsp/ExtrusionEntityCollection.xsp b/xs/xsp/ExtrusionEntityCollection.xsp
index 1021b56f1..09296fcb0 100644
--- a/xs/xsp/ExtrusionEntityCollection.xsp
+++ b/xs/xsp/ExtrusionEntityCollection.xsp
@@ -93,7 +93,6 @@ ExtrusionEntityCollection::chained_path_indices(bool no_reverse)
         const char* CLASS = "Slic3r::ExtrusionPath::Collection";
     CODE:
         RETVAL = new ExtrusionEntityCollection();
-        std::vector<size_t> indices;
         THIS->chained_path(RETVAL, no_reverse, &RETVAL->orig_indices);
     OUTPUT:
         RETVAL