diff --git a/lib/Slic3r/GCode.pm b/lib/Slic3r/GCode.pm
index f1269debbb..6c34572f6f 100644
--- a/lib/Slic3r/GCode.pm
+++ b/lib/Slic3r/GCode.pm
@@ -1,7 +1,7 @@
 package Slic3r::GCode;
 use Moo;
 
-use List::Util qw(min first);
+use List::Util qw(min max first);
 use Slic3r::ExtrusionPath ':roles';
 use Slic3r::Flow ':roles';
 use Slic3r::Geometry qw(epsilon scale unscale scaled_epsilon points_coincide PI X Y B);
@@ -27,6 +27,7 @@ has 'speed'              => (is => 'rw');
 has '_extrusion_axis'    => (is => 'rw');
 has '_retract_lift'      => (is => 'rw');
 has 'extruders'          => (is => 'ro', default => sub {{}});
+has 'multiple_extruders' => (is => 'rw', default => sub {0});
 has 'extruder'           => (is => 'rw');
 has 'speeds'             => (is => 'lazy');  # mm/min
 has 'external_mp'        => (is => 'rw');
@@ -55,6 +56,11 @@ sub set_extruders {
         $self->extruders->{$i} = my $e = Slic3r::Extruder->new_from_config($self->print_config, $i);
         $self->enable_wipe(1) if $e->wipe;
     }
+    
+    # we enable support for multiple extruder if any extruder greater than 0 is used
+    # (even if prints only uses that one) since we need to output Tx commands
+    # first extruder has index 0
+    $self->multiple_extruders(max(@$extruder_ids) > 0);
 }
 
 sub _build_speeds {
@@ -81,11 +87,6 @@ my %role_speeds = (
     &EXTR_ROLE_GAPFILL                      => 'gap_fill',
 );
 
-sub multiple_extruders {
-    my $self = shift;
-    return (keys %{$self->extruders}) > 1;
-}
-
 sub set_shift {
     my ($self, @shift) = @_;
     
diff --git a/lib/Slic3r/GUI/Plater/ObjectPartsPanel.pm b/lib/Slic3r/GUI/Plater/ObjectPartsPanel.pm
index 31b7dc03db..b911c8141c 100644
--- a/lib/Slic3r/GUI/Plater/ObjectPartsPanel.pm
+++ b/lib/Slic3r/GUI/Plater/ObjectPartsPanel.pm
@@ -162,7 +162,7 @@ sub selection_changed {
             $material //= $volume->assign_unique_material;
             $self->{staticbox}->SetLabel('Part Settings');
             $self->{settings_panel}->enable;
-            $self->{settings_panel}->set_opt_keys(Slic3r::Config::PrintRegion->new->get_keys);
+            $self->{settings_panel}->set_opt_keys([ 'extruder', @{Slic3r::Config::PrintRegion->new->get_keys} ]);
             $self->{settings_panel}->set_config($material->config);
         } elsif ($itemData->{type} eq 'object') {
             # select all object volumes in 3D preview
@@ -174,7 +174,7 @@ sub selection_changed {
             $self->{staticbox}->SetLabel('Object Settings');
             $self->{settings_panel}->enable;
             $self->{settings_panel}->set_opt_keys(
-                [ map @{$_->get_keys}, Slic3r::Config::PrintObject->new, Slic3r::Config::PrintRegion->new ]
+                [ 'extruder', map @{$_->get_keys}, Slic3r::Config::PrintObject->new, Slic3r::Config::PrintRegion->new ]
             );
             $self->{settings_panel}->set_config($self->{model_object}->config);
         }
diff --git a/lib/Slic3r/GUI/Tab.pm b/lib/Slic3r/GUI/Tab.pm
index 19af91f481..2fdf93559a 100644
--- a/lib/Slic3r/GUI/Tab.pm
+++ b/lib/Slic3r/GUI/Tab.pm
@@ -528,7 +528,7 @@ sub build {
     
     $self->add_options_page('Multiple Extruders', 'funnel.png', optgroups => [
         {
-            title => 'Override extruders',
+            title => 'Extruders',
             options => [qw(perimeter_extruder infill_extruder support_material_extruder support_material_interface_extruder)],
         },
         {
diff --git a/lib/Slic3r/Print.pm b/lib/Slic3r/Print.pm
index b2a3be6250..c9b52f6e80 100644
--- a/lib/Slic3r/Print.pm
+++ b/lib/Slic3r/Print.pm
@@ -32,6 +32,9 @@ has 'brim' => (is => 'rw', default => sub { Slic3r::ExtrusionPath::Collection->n
 sub apply_config {
     my ($self, $config) = @_;
     
+    $config = $config->clone;
+    $config->normalize;
+    
     # apply variables to placeholder parser
     $self->placeholder_parser->apply_config($config);
     
@@ -52,7 +55,9 @@ sub apply_config {
         my $new = $self->default_object_config->clone;
         
         # we override the new config with object-specific options
-        $new->apply_dynamic($object->model_object->config);
+        my $model_object_config = $object->model_object->config->clone;
+        $model_object_config->normalize;
+        $new->apply_dynamic($model_object_config);
         
         # check whether the new config is different from the current one
         my $diff = $object->config->diff($new);
@@ -66,55 +71,42 @@ sub apply_config {
     # handle changes to regions config defaults
     $self->default_region_config->apply_dynamic($config);
     
-    # check whether after applying the new region config defaults to all existing regions
-    # they still have distinct configs; if not we need to re-add objects in order to 
-    # merge the now-equal regions
-    
-    # first compute the transformed region configs
-    my @new_region_configs = ();
-    foreach my $region_id (0..$#{$self->regions}) {
-        my $new = $self->default_region_config->clone;
+    # All regions now have distinct settings.
+    # Check whether applying the new region config defaults we'd get different regions.
+    my $rearrange_regions = 0;
+    REGION: foreach my $region_id (0..$#{$self->regions}) {
         foreach my $object (@{$self->objects}) {
             foreach my $volume_id (@{ $object->region_volumes->[$region_id] }) {
                 my $volume = $object->model_object->volumes->[$volume_id];
-                next if !defined $volume->material_id;
-                my $material = $object->model_object->model->materials->{$volume->material_id};
-                $new->apply_dynamic($material->config);
-                push @new_region_configs, $new;
+                
+                my $new = $self->default_region_config->clone;
+                {
+                    my $model_object_config = $object->model_object->config->clone;
+                    $model_object_config->normalize;
+                    $new->apply_dynamic($model_object_config);
+                }
+                if (defined $volume->material_id) {
+                    my $material_config = $object->model_object->model->materials->{$volume->material_id}->config->clone;
+                    $material_config->normalize;
+                    $new->apply_dynamic($material_config);
+                }
+                if (!$new->equals($self->regions->[$region_id]->config)) {
+                    $rearrange_regions = 1;
+                    last REGION;
+                }
             }
         }
     }
     
-    # then find the first pair of identical configs
-    my $have_identical_configs = 0;
-    my $region_diff = [];
-    for my $i (0..$#new_region_configs) {
-        for my $j (($i+1)..$#new_region_configs) {
-            if ($new_region_configs[$i]->equals($new_region_configs[$j])) {
-                $have_identical_configs = 1;
-            }
-        }
-        my $diff = $self->regions->[$i]->config->diff($new_region_configs[$i]);
-        push @$region_diff, @$diff;
-    }
-    
-    if ($have_identical_configs) {
-        # okay, the current subdivision of regions does not make sense anymore.
+    # Some optimization is possible: if the volumes-regions mappings don't change
+    # but still region configs are changed somehow, we could just apply the diff
+    # and invalidate the affected steps.
+    if ($rearrange_regions) {
+        # the current subdivision of regions does not make sense anymore.
         # we need to remove all objects and re-add them
         my @model_objects = map $_->model_object, @{$self->objects};
         $self->delete_all_objects;
         $self->add_model_object($_) for @model_objects;
-    } elsif (@$region_diff > 0) {
-        # if there are no identical regions even after applying the change in 
-        # region config defaults, but at least one region config option changed,
-        # store the new region configs and invalidate
-        # the affected step(s)
-        foreach my $region_id (0..$#{$self->regions}) {
-            $self->regions->[$region_id]->config->apply($new_region_configs[$region_id]);
-        }
-        
-        # TODO: only invalidate changed steps
-        $_->_state->invalidate_all for @{$self->objects};
     }
 }
 
@@ -131,6 +123,9 @@ sub add_model_object {
     my $self = shift;
     my ($object, $obj_idx) = @_;
     
+    my $object_config = $object->config->clone;
+    $object_config->normalize;
+    
     my %volumes = ();           # region_id => [ volume_id, ... ]
     foreach my $volume_id (0..$#{$object->volumes}) {
         my $volume = $object->volumes->[$volume_id];
@@ -140,10 +135,11 @@ sub add_model_object {
         $config->apply($self->default_region_config);
         
         # override the defaults with per-object config and then with per-material config
-        $config->apply_dynamic($object->config);
+        $config->apply_dynamic($object_config);
         
         if (defined $volume->material_id) {
-            my $material_config = $object->model->materials->{ $volume->material_id }->config;
+            my $material_config = $object->model->materials->{ $volume->material_id }->config->clone;
+            $material_config->normalize;
             $config->apply_dynamic($material_config);
         }
         
@@ -182,7 +178,7 @@ sub add_model_object {
     
     # apply config to print object
     $o->config->apply($self->default_object_config);
-    $o->config->apply_dynamic($object->config);
+    $o->config->apply_dynamic($object_config);
     
     # store print object at the given position
     if (defined $obj_idx) {
@@ -1102,6 +1098,9 @@ sub invalidate_step {
 sub auto_assign_extruders {
     my ($self, $model_object) = @_;
     
+    # only assign extruders if object has more than one volume
+    return if @{$model_object->volumes} == 1;
+    
     my $extruders = scalar @{ $self->config->nozzle_diameter };
     foreach my $i (0..$#{$model_object->volumes}) {
         my $volume = $model_object->volumes->[$i];
diff --git a/lib/Slic3r/Test.pm b/lib/Slic3r/Test.pm
index b9d3d9aa1c..e4663afbc9 100644
--- a/lib/Slic3r/Test.pm
+++ b/lib/Slic3r/Test.pm
@@ -108,7 +108,8 @@ sub model {
     
     my $model = Slic3r::Model->new;
     my $object = $model->add_object(input_file => "${model_name}.stl");
-    $object->add_volume(mesh => mesh($model_name, %params));
+    $model->set_material($model_name);
+    $object->add_volume(mesh => mesh($model_name, %params), material_id => $model_name);
     $object->add_instance(
         offset      => [0,0],
         rotation    => $params{rotation} // 0,
@@ -134,7 +135,10 @@ sub init_print {
         }
         $model->arrange_objects($print->config->min_object_distance);
         $model->center_instances_around_point($print->config->print_center);
-        $print->add_model_object($_) for @{$model->objects};
+        foreach my $model_object (@{$model->objects}) {
+            $print->auto_assign_extruders($model_object);
+            $print->add_model_object($model_object);
+        }
     }
     $print->validate;
     
diff --git a/t/print.t b/t/print.t
index 746ce5d3c2..863c17252e 100644
--- a/t/print.t
+++ b/t/print.t
@@ -1,4 +1,4 @@
-use Test::More tests => 3;
+use Test::More tests => 5;
 use strict;
 use warnings;
 
@@ -35,16 +35,24 @@ use Slic3r::Test;
     my $config = Slic3r::Config->new_from_defaults;
     
     # user adds one object to the plater
-    my $print = Slic3r::Test::init_print('20mm_cube', config => $config);
+    my $print = Slic3r::Test::init_print(my $model = Slic3r::Test::model('20mm_cube'), config => $config);
     
-    # user sets a per-object option
-    $print->objects->[0]->config->set('fill_density', 100);
+    # user sets a per-region option
+    $print->objects->[0]->model_object->config->set('fill_density', 100);
     $print->reload_object(0);
     
     # user exports G-code, thus the default config is reapplied
     $print->apply_config($config);
     
-    is $print->objects->[0]->config->fill_density, 100, 'apply_config() does not override per-object settings';
+    is $print->regions->[0]->config->fill_density, 100, 'apply_config() does not override per-object settings';
+    
+    # user assigns object extruders
+    $print->objects->[0]->model_object->config->set('extruder', 3);
+    $print->objects->[0]->model_object->config->set('perimeter_extruder', 2);
+    $print->reload_object(0);
+    
+    is $print->regions->[0]->config->infill_extruder, 3, 'extruder setting is correctly expanded';
+    is $print->regions->[0]->config->perimeter_extruder, 2, 'extruder setting does not override explicitely specified extruders';
 }
 
 __END__
diff --git a/xs/src/PrintConfig.cpp b/xs/src/PrintConfig.cpp
index 99dd8535ae..711740897d 100644
--- a/xs/src/PrintConfig.cpp
+++ b/xs/src/PrintConfig.cpp
@@ -4,44 +4,4 @@ namespace Slic3r {
 
 t_optiondef_map PrintConfigDef::def = PrintConfigDef::build_def();
 
-void
-StaticPrintConfig::prepare_extruder_option(const t_config_option_key opt_key, DynamicPrintConfig& other)
-{
-    // don't apply role-based extruders if their value is zero
-    if (other.has(opt_key) && other.option(opt_key)->getInt() == 0)
-        other.erase(opt_key);
-    
-    // only apply default extruder if our role-based value is zero
-    // (i.e. default extruder has the lowest priority among all other values)
-    if (other.has("extruder")) {
-        int extruder = other.option("extruder")->getInt();
-        if (extruder > 0) {
-            if (!other.has(opt_key) && this->option(opt_key)->getInt() == 0)
-                other.option(opt_key, true)->setInt(extruder);
-        }
-    }
-}
-
-void
-PrintObjectConfig::apply(const ConfigBase &other, bool ignore_nonexistent) {
-    DynamicPrintConfig other_clone;
-    other_clone.apply(other);
-    
-    this->prepare_extruder_option("support_material_extruder", other_clone);
-    this->prepare_extruder_option("support_material_interface_extruder", other_clone);
-    
-    StaticConfig::apply(other_clone, ignore_nonexistent);
-};
-
-void
-PrintRegionConfig::apply(const ConfigBase &other, bool ignore_nonexistent) {
-    DynamicPrintConfig other_clone;
-    other_clone.apply(other);
-    
-    this->prepare_extruder_option("infill_extruder", other_clone);
-    this->prepare_extruder_option("perimeter_extruder", other_clone);
-    
-    StaticConfig::apply(other_clone, ignore_nonexistent);
-};
-
 }
diff --git a/xs/src/PrintConfig.hpp b/xs/src/PrintConfig.hpp
index 26012c1bfc..646c525983 100644
--- a/xs/src/PrintConfig.hpp
+++ b/xs/src/PrintConfig.hpp
@@ -399,10 +399,9 @@ class PrintConfigDef
         Options["infill_extruder"].type = coInt;
         Options["infill_extruder"].label = "Infill extruder";
         Options["infill_extruder"].category = "Extruders";
-        Options["infill_extruder"].tooltip = "The extruder to use when printing infill. First extruder is 1, while zero means use default extruder.";
-        Options["infill_extruder"].sidetext = "(leave 0 for default)";
+        Options["infill_extruder"].tooltip = "The extruder to use when printing infill.";
         Options["infill_extruder"].cli = "infill-extruder=i";
-        Options["infill_extruder"].min = 0;
+        Options["infill_extruder"].min = 1;
 
         Options["infill_extrusion_width"].type = coFloatOrPercent;
         Options["infill_extrusion_width"].label = "Infill";
@@ -524,11 +523,10 @@ class PrintConfigDef
         Options["perimeter_extruder"].type = coInt;
         Options["perimeter_extruder"].label = "Perimeter extruder";
         Options["perimeter_extruder"].category = "Extruders";
-        Options["perimeter_extruder"].tooltip = "The extruder to use when printing perimeters. First extruder is 1, while zero means use default extruder.";
-        Options["perimeter_extruder"].sidetext = "(leave 0 for default)";
+        Options["perimeter_extruder"].tooltip = "The extruder to use when printing perimeters. First extruder is 1.";
         Options["perimeter_extruder"].cli = "perimeter-extruder=i";
         Options["perimeter_extruder"].aliases.push_back("perimeters_extruder");
-        Options["perimeter_extruder"].min = 0;
+        Options["perimeter_extruder"].min = 1;
 
         Options["perimeter_extrusion_width"].type = coFloatOrPercent;
         Options["perimeter_extrusion_width"].label = "Perimeters";
@@ -774,10 +772,9 @@ class PrintConfigDef
         Options["support_material_extruder"].type = coInt;
         Options["support_material_extruder"].label = "Support material extruder";
         Options["support_material_extruder"].category = "Extruders";
-        Options["support_material_extruder"].tooltip = "The extruder to use when printing support material. This affects brim and raft too. First extruder is 1, while zero means use default extruder.";
-        Options["support_material_extruder"].sidetext = "(leave 0 for default)";
+        Options["support_material_extruder"].tooltip = "The extruder to use when printing support material. This affects brim and raft too.";
         Options["support_material_extruder"].cli = "support-material-extruder=i";
-        Options["support_material_extruder"].min = 0;
+        Options["support_material_extruder"].min = 1;
 
         Options["support_material_extrusion_width"].type = coFloatOrPercent;
         Options["support_material_extrusion_width"].label = "Support material";
@@ -789,10 +786,9 @@ class PrintConfigDef
         Options["support_material_interface_extruder"].type = coInt;
         Options["support_material_interface_extruder"].label = "Support material interface extruder";
         Options["support_material_interface_extruder"].category = "Extruders";
-        Options["support_material_interface_extruder"].tooltip = "The extruder to use when printing support material interface. This affects raft too. First extruder is 1, while zero means use default extruder.";
-        Options["support_material_interface_extruder"].sidetext = "(leave 0 for default)";
+        Options["support_material_interface_extruder"].tooltip = "The extruder to use when printing support material interface. This affects raft too.";
         Options["support_material_interface_extruder"].cli = "support-material-interface-extruder=i";
-        Options["support_material_interface_extruder"].min = 0;
+        Options["support_material_interface_extruder"].min = 1;
 
         Options["support_material_interface_layers"].type = coInt;
         Options["support_material_interface_layers"].label = "Interface layers";
@@ -940,6 +936,21 @@ class DynamicPrintConfig : public DynamicConfig
     DynamicPrintConfig() {
         this->def = &PrintConfigDef::def;
     };
+    
+    void normalize() {
+        if (this->has("extruder")) {
+            int extruder = this->option("extruder")->getInt();
+            this->erase("extruder");
+            if (!this->has("infill_extruder"))
+                this->option("infill_extruder", true)->setInt(extruder);
+            if (!this->has("perimeter_extruder"))
+                this->option("infill_extruder", true)->setInt(extruder);
+            if (!this->has("support_material_extruder"))
+                this->option("support_material_extruder", true)->setInt(extruder);
+            if (!this->has("support_material_interface_extruder"))
+                this->option("support_material_interface_extruder", true)->setInt(extruder);
+        }
+    };
 };
 
 class StaticPrintConfig : public virtual StaticConfig
@@ -948,9 +959,6 @@ class StaticPrintConfig : public virtual StaticConfig
     StaticPrintConfig() {
         this->def = &PrintConfigDef::def;
     };
-    
-    protected:
-    void prepare_extruder_option(const t_config_option_key opt_key, DynamicPrintConfig& other);
 };
 
 class PrintObjectConfig : public virtual StaticPrintConfig
@@ -987,10 +995,10 @@ class PrintObjectConfig : public virtual StaticPrintConfig
         this->support_material.value                             = false;
         this->support_material_angle.value                       = 0;
         this->support_material_enforce_layers.value              = 0;
-        this->support_material_extruder.value                    = 0;
+        this->support_material_extruder.value                    = 1;
         this->support_material_extrusion_width.value             = 0;
         this->support_material_extrusion_width.percent           = false;
-        this->support_material_interface_extruder.value          = 0;
+        this->support_material_interface_extruder.value          = 1;
         this->support_material_interface_layers.value            = 3;
         this->support_material_interface_spacing.value           = 0;
         this->support_material_pattern.value                     = smpHoneycomb;
@@ -1021,8 +1029,6 @@ class PrintObjectConfig : public virtual StaticPrintConfig
         
         return NULL;
     };
-    
-    void apply(const ConfigBase &other, bool ignore_nonexistent = false);
 };
 
 class PrintRegionConfig : public virtual StaticPrintConfig
@@ -1053,11 +1059,11 @@ class PrintRegionConfig : public virtual StaticPrintConfig
         this->fill_angle.value                                   = 45;
         this->fill_density.value                                 = 40;
         this->fill_pattern.value                                 = ipHoneycomb;
-        this->infill_extruder.value                              = 0;
+        this->infill_extruder.value                              = 1;
         this->infill_extrusion_width.value                       = 0;
         this->infill_extrusion_width.percent                     = false;
         this->infill_every_layers.value                          = 1;
-        this->perimeter_extruder.value                           = 0;
+        this->perimeter_extruder.value                           = 1;
         this->perimeter_extrusion_width.value                    = 0;
         this->perimeter_extrusion_width.percent                  = false;
         this->perimeters.value                                   = 3;
@@ -1094,8 +1100,6 @@ class PrintRegionConfig : public virtual StaticPrintConfig
         
         return NULL;
     };
-    
-    void apply(const ConfigBase &other, bool ignore_nonexistent = false);
 };
 
 class PrintConfig : public virtual StaticPrintConfig
@@ -1398,12 +1402,6 @@ class FullPrintConfig : public PrintObjectConfig, public PrintRegionConfig, publ
         if ((opt = PrintConfig::option(opt_key, create)) != NULL) return opt;
         return NULL;
     };
-    
-    void apply(const ConfigBase &other, bool ignore_nonexistent = false) {
-        PrintObjectConfig::apply(other, ignore_nonexistent);
-        PrintRegionConfig::apply(other, ignore_nonexistent);
-        PrintConfig::apply(other, ignore_nonexistent);
-    };
 };
 
 }
diff --git a/xs/t/15_config.t b/xs/t/15_config.t
index b1e2391f20..347e68edf6 100644
--- a/xs/t/15_config.t
+++ b/xs/t/15_config.t
@@ -4,7 +4,7 @@ use strict;
 use warnings;
 
 use Slic3r::XS;
-use Test::More tests => 99;
+use Test::More tests => 94;
 
 foreach my $config (Slic3r::Config->new, Slic3r::Config::Full->new) {
     $config->set('layer_height', 0.3);
@@ -126,64 +126,6 @@ foreach my $config (Slic3r::Config->new, Slic3r::Config::Full->new) {
     is $config->get('fill_pattern'), 'line', 'no interferences between DynamicConfig objects';
 }
 
-{
-    {
-        my $config = Slic3r::Config->new;
-        $config->set('infill_extruder', 2);
-        my $config2 = Slic3r::Config::PrintRegion->new;
-        $config2->apply($config);
-        is $config2->get('infill_extruder'), $config->get('infill_extruder'),
-            'non-zero infill_extruder is applied';
-    }
-    {
-        my $config = Slic3r::Config->new;
-        $config->set('infill_extruder', 0);
-        my $config2 = Slic3r::Config::PrintRegion->new;
-        $config2->set('infill_extruder', 3);
-        $config2->apply($config);
-        isnt $config2->get('infill_extruder'), $config->get('infill_extruder'),
-            'zero infill_extruder is not applied';
-    }
-    {
-        my $config = Slic3r::Config->new;
-        $config->set('extruder', 3);
-        my $config2 = Slic3r::Config::PrintRegion->new;
-        $config2->set('infill_extruder', 2);
-        $config2->apply($config);
-        is $config2->get('infill_extruder'), 2, 'extruder does not overwrite non-zero role extruders';
-        is $config2->get('perimeter_extruder'), 3, 'extruder overwrites zero role extruders';
-    }
-}
-
-{
-    {
-        my $config = Slic3r::Config->new;
-        $config->set('support_material_extruder', 2);
-        my $config2 = Slic3r::Config::PrintObject->new;
-        $config2->apply($config);
-        is $config2->get('support_material_extruder'), $config->get('support_material_extruder'),
-            'non-zero support_material_extruder is applied';
-    }
-    {
-        my $config = Slic3r::Config->new;
-        $config->set('support_material_extruder', 0);
-        my $config2 = Slic3r::Config::PrintObject->new;
-        $config2->set('support_material_extruder', 3);
-        $config2->apply($config);
-        isnt $config2->get('support_material_extruder'), $config->get('support_material_extruder'),
-            'zero support_material_extruder is not applied';
-    }
-    {
-        my $config = Slic3r::Config->new;
-        $config->set('extruder', 3);
-        my $config2 = Slic3r::Config::PrintObject->new;
-        $config2->set('support_material_extruder', 2);
-        $config2->apply($config);
-        is $config2->get('support_material_extruder'), 2, 'extruder does not overwrite non-zero role extruders';
-        is $config2->get('support_material_interface_extruder'), 3, 'extruder overwrites zero role extruders';
-    }
-}
-
 {
     my $config = Slic3r::Config->new;
     # the pair [0,0] is part of the test, since it checks whether the 0x0 serialized value is correctly parsed
@@ -193,4 +135,14 @@ foreach my $config (Slic3r::Config->new, Slic3r::Config::Full->new) {
     is_deeply $config->get('extruder_offset'), $config2->get('extruder_offset'), 'apply dynamic over dynamic';
 }
 
+{
+    my $config = Slic3r::Config->new;
+    $config->set('extruder', 2);
+    $config->set('perimeter_extruder', 3);
+    $config->normalize;
+    ok !$config->has('extruder'), 'extruder option is removed after normalize()';
+    is $config->get('infill_extruder'), 2, 'undefined extruder is populated with default extruder';
+    is $config->get('perimeter_extruder'), 3, 'defined extruder is not overwritten by default extruder';
+}
+
 __END__
diff --git a/xs/xsp/Config.xsp b/xs/xsp/Config.xsp
index b7cb8ea3a7..5a9a0b13c0 100644
--- a/xs/xsp/Config.xsp
+++ b/xs/xsp/Config.xsp
@@ -25,6 +25,7 @@
     std::vector<std::string> get_keys()
         %code{% THIS->keys(&RETVAL); %};
     void erase(t_config_option_key opt_key);
+    void normalize();
 };
 
 %name{Slic3r::Config::Print} class PrintConfig {