diff --git a/lib/Slic3r/Fill.pm b/lib/Slic3r/Fill.pm
index e3acbe551..09fba7a29 100644
--- a/lib/Slic3r/Fill.pm
+++ b/lib/Slic3r/Fill.pm
@@ -49,9 +49,10 @@ sub make_fill {
     
     Slic3r::debugf "Filling layer %d:\n", $layerm->id;
     
-    my $fill_density        = $layerm->config->fill_density;
-    my $infill_flow         = $layerm->flow(FLOW_ROLE_INFILL);
-    my $solid_infill_flow   = $layerm->flow(FLOW_ROLE_SOLID_INFILL);
+    my $fill_density            = $layerm->config->fill_density;
+    my $infill_flow             = $layerm->flow(FLOW_ROLE_INFILL);
+    my $solid_infill_flow       = $layerm->flow(FLOW_ROLE_SOLID_INFILL);
+    my $top_solid_infill_flow   = $layerm->flow(FLOW_ROLE_TOP_SOLID_INFILL);
     
     my @surfaces = ();
     
@@ -75,7 +76,7 @@ sub make_fill {
                 if ($groups[$i][0]->is_solid && (!$groups[$i][0]->is_bridge || $layerm->id == 0)) {
                     $is_solid[$i] = 1;
                     $fw[$i] = ($groups[$i][0]->surface_type == S_TYPE_TOP)
-                        ? $layerm->flow(FLOW_ROLE_TOP_SOLID_INFILL)->width
+                        ? $top_solid_infill_flow->width
                         : $solid_infill_flow->width;
                     $pattern[$i] = $groups[$i][0]->is_external
                         ? $layerm->config->external_fill_pattern
diff --git a/lib/Slic3r/GUI/Tab.pm b/lib/Slic3r/GUI/Tab.pm
index d40763df4..00eb1d6fa 100644
--- a/lib/Slic3r/GUI/Tab.pm
+++ b/lib/Slic3r/GUI/Tab.pm
@@ -745,11 +745,13 @@ sub _update {
             perimeter_speed small_perimeter_speed external_perimeter_speed);
     
     my $have_infill = $config->fill_density > 0;
+    # infill_extruder uses the same logic as in Print::extruders()
     $self->get_field($_)->toggle($have_infill)
         for qw(fill_pattern infill_every_layers infill_only_where_needed solid_infill_every_layers
             solid_infill_below_area infill_extruder);
     
     my $have_solid_infill = ($config->top_solid_layers > 0) || ($config->bottom_solid_layers > 0);
+    # solid_infill_extruder uses the same logic as in Print::extruders()
     $self->get_field($_)->toggle($have_solid_infill)
         for qw(external_fill_pattern infill_first solid_infill_extruder solid_infill_extrusion_width
             solid_infill_speed);
@@ -772,6 +774,7 @@ sub _update {
         for qw(skirt_distance skirt_height);
     
     my $have_brim = $config->brim_width > 0;
+    # perimeter_extruder uses the same logic as in Print::extruders()
     $self->get_field('perimeter_extruder')->toggle($have_perimeters || $have_brim);
     
     my $have_support_material = $config->support_material || $config->raft_layers > 0;
diff --git a/t/fill.t b/t/fill.t
index e43bdaadc..6fb05196e 100644
--- a/t/fill.t
+++ b/t/fill.t
@@ -12,7 +12,7 @@ BEGIN {
 use List::Util qw(first sum);
 use Slic3r;
 use Slic3r::Geometry qw(X Y scale unscale convex_hull);
-use Slic3r::Geometry::Clipper qw(union diff_ex offset);
+use Slic3r::Geometry::Clipper qw(union diff diff_ex offset offset2_ex);
 use Slic3r::Surface qw(:types);
 use Slic3r::Test;
 
@@ -248,18 +248,27 @@ for my $pattern (qw(rectilinear honeycomb hilbertcurve concentric)) {
 {
     my $config = Slic3r::Config->new_from_defaults;
     $config->set('skirts', 0);
-    $config->set('perimeters', 0);
+    $config->set('perimeters', 1);
     $config->set('fill_density', 0);
     $config->set('top_solid_layers', 0);
     $config->set('bottom_solid_layers', 0);
     $config->set('solid_infill_below_area', 20000000);
     $config->set('solid_infill_every_layers', 2);
+    $config->set('perimeter_speed', 99);
+    $config->set('external_perimeter_speed', 99);
+    $config->set('cooling', 0);
+    $config->set('first_layer_speed', '100%');
     
     my $print = Slic3r::Test::init_print('20mm_cube', config => $config);
     my %layers_with_extrusion = ();
     Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
         my ($self, $cmd, $args, $info) = @_;
-        $layers_with_extrusion{$self->Z} = 1 if $info->{extruding};
+        
+        if ($cmd eq 'G1' && $info->{dist_XY} > 0 && $info->{extruding}) {
+            if (($args->{F} // $self->F) != $config->perimeter_speed*60) {
+                $layers_with_extrusion{$self->Z} = ($args->{F} // $self->F);
+            }
+        }
     });
     
     ok !%layers_with_extrusion,
@@ -275,6 +284,7 @@ for my $pattern (qw(rectilinear honeycomb hilbertcurve concentric)) {
     $config->set('first_layer_height', 0.2);
     $config->set('nozzle_diameter', [0.35]);
     $config->set('infill_extruder', 2);
+    $config->set('solid_infill_extruder', 2);
     $config->set('infill_extrusion_width', 0.52);
     $config->set('solid_infill_extrusion_width', 0.52);
     $config->set('first_layer_extrusion_width', 0);
@@ -301,7 +311,9 @@ for my $pattern (qw(rectilinear honeycomb hilbertcurve concentric)) {
     my $grow_d = scale($config->infill_extrusion_width)/2;
     my $layer0_infill = union([ map @{$_->grow($grow_d)}, @{ $infill{0.2} } ]);
     my $layer1_infill = union([ map @{$_->grow($grow_d)}, @{ $infill{0.4} } ]);
-    my $diff = [ grep { $_->area > 2*(($grow_d*2)**2) } @{diff_ex($layer0_infill, $layer1_infill)} ];
+    my $diff = diff($layer0_infill, $layer1_infill);
+    $diff = offset2_ex($diff, -$grow_d, +$grow_d);
+    $diff = [ grep { $_->area > 2*(($grow_d*2)**2) } @$diff ];
     is scalar(@$diff), 0, 'no missing parts in solid shell when fill_density is 0';
 }
 
diff --git a/t/perimeters.t b/t/perimeters.t
index 11cc0cbd4..ed6f6b430 100644
--- a/t/perimeters.t
+++ b/t/perimeters.t
@@ -229,19 +229,19 @@ use Slic3r::Test;
     
     my $test = sub {
         my ($print) = @_;
-        my $has_bridges = 0;
+        my %z_with_bridges = ();  # z => 1
         Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
             my ($self, $cmd, $args, $info) = @_;
         
             if ($info->{extruding} && $info->{dist_XY} > 0) {
-                $has_bridges++ if ($args->{F} // $self->F) == $config->bridge_speed*60;
+                $z_with_bridges{$self->Z} = 1 if ($args->{F} // $self->F) == $config->bridge_speed*60;
             }
         });
-        return $has_bridges;
+        return scalar keys %z_with_bridges;
     };
-    ok !$test->(Slic3r::Test::init_print('V', config => $config)),
-        'no overhangs printed with bridge speed';
-    ok $test->(Slic3r::Test::init_print('V', config => $config, scale_xyz => [3,1,1])),
+    ok $test->(Slic3r::Test::init_print('V', config => $config)) == 1,
+        'no overhangs printed with bridge speed';  # except for the first internal solid layers above void
+    ok $test->(Slic3r::Test::init_print('V', config => $config, scale_xyz => [3,1,1])) > 1,
         'overhangs printed with bridge speed';
 }
 
diff --git a/t/shells.t b/t/shells.t
index a12858ae0..f3fd62d14 100644
--- a/t/shells.t
+++ b/t/shells.t
@@ -72,6 +72,9 @@ use Slic3r::Test;
     $config->set('bottom_solid_layers', 0);
     ok $test->(), "no shells are applied when both top and bottom are set to zero";
     
+    $config->set('perimeters', 1);
+    $config->set('top_solid_layers', 3);
+    $config->set('bottom_solid_layers', 3);
     $config->set('fill_density', 0);
     ok $test->(), "proper number of shells is applied even when fill density is none";
 }
diff --git a/t/support.t b/t/support.t
index 5ecf27b0c..2091b4432 100644
--- a/t/support.t
+++ b/t/support.t
@@ -1,4 +1,4 @@
-use Test::More tests => 24;
+use Test::More tests => 25;
 use strict;
 use warnings;
 
@@ -179,7 +179,7 @@ use Slic3r::Test;
     $test->(70);
 }
 
-TTT: {
+{
     my $config = Slic3r::Config->new_from_defaults;
     $config->set('brim_width',  0);
     $config->set('skirts', 0);
@@ -219,4 +219,14 @@ TTT: {
     ok !$test->(), 'bridge speed is not used when raft_layers > 0 and support_material_contact_distance == 0';
 }
 
+{
+    my $config = Slic3r::Config->new_from_defaults;
+    $config->set('raft_layers', 3);
+    $config->set('nozzle_diameter', [0.4, 1]);
+    $config->set('first_layer_height', 0.8);
+    $config->set('support_material_extruder', 2);
+    my $print = Slic3r::Test::init_print('20mm_cube', config => $config);
+    ok Slic3r::Test::gcode($print), 'first_layer_height is validated with support material extruder nozzle diameter when using raft layers';
+}
+
 __END__
diff --git a/xs/src/libslic3r/Print.cpp b/xs/src/libslic3r/Print.cpp
index 2128095fa..d3bb43b3c 100644
--- a/xs/src/libslic3r/Print.cpp
+++ b/xs/src/libslic3r/Print.cpp
@@ -305,9 +305,16 @@ Print::extruders() const
     std::set<size_t> extruders;
     
     FOREACH_REGION(this, region) {
-        extruders.insert((*region)->config.perimeter_extruder - 1);
-        extruders.insert((*region)->config.infill_extruder - 1);
-        extruders.insert((*region)->config.solid_infill_extruder - 1);
+        // these checks reflect the same logic used in the GUI for enabling/disabling
+        // extruder selection fields
+        if ((*region)->config.perimeters.value > 0 || this->config.brim_width.value > 0)
+            extruders.insert((*region)->config.perimeter_extruder - 1);
+        
+        if ((*region)->config.fill_density.value > 0)
+            extruders.insert((*region)->config.infill_extruder - 1);
+        
+        if ((*region)->config.top_solid_layers.value > 0 || (*region)->config.bottom_solid_layers.value > 0)
+            extruders.insert((*region)->config.solid_infill_extruder - 1);
     }
     FOREACH_OBJECT(this, object) {
         if ((*object)->has_support_material()) {
@@ -619,17 +626,37 @@ Print::validate() const
     }
     
     {
-        std::vector<double> layer_heights;
+        // find the smallest nozzle diameter
+        std::set<size_t> extruders = this->extruders();
+        if (extruders.empty())
+            throw PrintValidationException("The supplied settings will cause an empty print.");
+        
+        std::set<double> nozzle_diameters;
+        for (std::set<size_t>::iterator it = extruders.begin(); it != extruders.end(); ++it)
+            nozzle_diameters.insert(this->config.nozzle_diameter.get_at(*it));
+        double min_nozzle_diameter = *std::min_element(nozzle_diameters.begin(), nozzle_diameters.end());
+        
         FOREACH_OBJECT(this, i_object) {
             PrintObject* object = *i_object;
-            layer_heights.push_back(object->config.layer_height);
-            layer_heights.push_back(object->config.get_abs_value("first_layer_height"));
-        }
-        double max_layer_height = *std::max_element(layer_heights.begin(), layer_heights.end());
-        
-        std::set<size_t> extruders = this->extruders();
-        for (std::set<size_t>::iterator it = extruders.begin(); it != extruders.end(); ++it) {
-            if (max_layer_height > this->config.nozzle_diameter.get_at(*it))
+            
+            // validate first_layer_height
+            double first_layer_height = object->config.get_abs_value("first_layer_height");
+            double first_layer_min_nozzle_diameter;
+            if (object->config.raft_layers > 0) {
+                // if we have raft layers, only support material extruder is used on first layer
+                size_t first_layer_extruder = object->config.raft_layers == 1
+                    ? object->config.support_material_interface_extruder-1
+                    : object->config.support_material_extruder-1;
+                first_layer_min_nozzle_diameter = this->config.nozzle_diameter.get_at(first_layer_extruder);
+            } else {
+                // if we don't have raft layers, any nozzle diameter is potentially used in first layer
+                first_layer_min_nozzle_diameter = min_nozzle_diameter;
+            }
+            if (first_layer_height > first_layer_min_nozzle_diameter)
+                throw PrintValidationException("First layer height can't be greater than nozzle diameter");
+            
+            // validate layer_height
+            if (object->config.layer_height.value > min_nozzle_diameter)
                 throw PrintValidationException("Layer height can't be greater than nozzle diameter");
         }
     }
diff --git a/xs/src/libslic3r/PrintObject.cpp b/xs/src/libslic3r/PrintObject.cpp
index 071247072..cf1ee20e4 100644
--- a/xs/src/libslic3r/PrintObject.cpp
+++ b/xs/src/libslic3r/PrintObject.cpp
@@ -348,7 +348,7 @@ PrintObject::bridge_over_infill()
         size_t region_id = region - this->_print->regions.begin();
         
         double fill_density = (*region)->config.fill_density.value;
-        if (fill_density == 100 || fill_density == 0) continue;
+        if (fill_density == 100) continue;
         
         FOREACH_LAYER(this, layer_it) {
             if (layer_it == this->layers.begin()) continue;