diff --git a/lib/Slic3r/Layer.pm b/lib/Slic3r/Layer.pm
index 5d36d0591..9d5259436 100644
--- a/lib/Slic3r/Layer.pm
+++ b/lib/Slic3r/Layer.pm
@@ -105,6 +105,8 @@ sub make_surfaces {
     my ($loops) = @_;
     
     {
+        # TODO: fix self-intersecting polygons in $loops (GH #160)
+        
         # merge everything
         my $expolygons = union_ex($loops);
         
@@ -130,7 +132,7 @@ sub make_surfaces {
         foreach my $contour (map $_->contour, @expolygons_without_holes) {
             foreach my $hole (grep !exists $bogus_holes{$_}, @reversed_holes) {
                 my $xor = xor_ex([$contour], [$hole]);
-                if (!@$xor || $area_sum->(@$xor) < scale 1) {  # TODO: define this threshold better
+                if ($area_sum->(@$xor) < scale 1) {  # TODO: define this threshold better
                     $bogus_holes{$hole} = $hole;
                 }
             }
@@ -170,10 +172,14 @@ sub make_surfaces {
             1,
         );
         
+        # TODO: remove very small expolygons from diff before attempting to do medial axis
+        # (benchmark first)
         push @{$self->thin_walls},
             grep $_,
             map $_->medial_axis(scale $Slic3r::flow_width),
             @$diff;
+        
+        Slic3r::debugf "  %d thin walls detected\n", scalar(@{$self->thin_walls}) if @{$self->thin_walls};
     }
     
     if (0) {
diff --git a/lib/Slic3r/Print.pm b/lib/Slic3r/Print.pm
index d962be62f..0f5045699 100644
--- a/lib/Slic3r/Print.pm
+++ b/lib/Slic3r/Print.pm
@@ -168,6 +168,7 @@ sub layer {
 
 sub detect_surfaces_type {
     my $self = shift;
+    Slic3r::debugf "Detecting solid surfaces...\n";
     
     # prepare a reusable subroutine to make surface differences
     my $surface_difference = sub {
@@ -184,7 +185,6 @@ sub detect_surfaces_type {
     
     for (my $i = 0; $i < $self->layer_count; $i++) {
         my $layer = $self->layers->[$i];
-        Slic3r::debugf "Detecting solid surfaces for layer %d\n", $layer->id;
         my $upper_layer = $self->layers->[$i+1];
         my $lower_layer = $i > 0 ? $self->layers->[$i-1] : undef;
         
@@ -225,8 +225,8 @@ sub detect_surfaces_type {
         # save surfaces to layer
         @{$layer->slices} = (@bottom, @top, @internal);
         
-        Slic3r::debugf "  layer %d has %d bottom, %d top and %d internal surfaces\n",
-            $layer->id, scalar(@bottom), scalar(@top), scalar(@internal);
+        Slic3r::debugf "  layer %d (%d sliced expolygons) has %d bottom, %d top and %d internal surfaces\n",
+            $layer->id, scalar(@{$layer->slices}), scalar(@bottom), scalar(@top), scalar(@internal);
     }
     
     # clip surfaces to the fill boundaries