diff --git a/lib/Slic3r/Print/SupportMaterial.pm b/lib/Slic3r/Print/SupportMaterial.pm
index 16c3b944c4..34829a2a2e 100644
--- a/lib/Slic3r/Print/SupportMaterial.pm
+++ b/lib/Slic3r/Print/SupportMaterial.pm
@@ -681,7 +681,7 @@ sub generate_toolpaths {
         # interface and contact infill
         if (@$interface || @$contact_infill) {
             $fillers{interface}->set_angle($interface_angle);
-            $fillers{interface}->set_spacing($_interface_flow->spacing);
+            $fillers{interface}->set_min_spacing($_interface_flow->spacing);
             
             # find centerline of the external loop
             $interface = offset2($interface, +scaled_epsilon, -(scaled_epsilon + $_interface_flow->scaled_width/2));
@@ -734,7 +734,7 @@ sub generate_toolpaths {
             
             # We don't use $base_flow->spacing because we need a constant spacing
             # value that guarantees that all layers are correctly aligned.
-            $filler->set_spacing($flow->spacing);
+            $filler->set_min_spacing($flow->spacing);
             
             my $density     = $support_density;
             my $base_flow   = $_flow;
@@ -753,7 +753,7 @@ sub generate_toolpaths {
                 
                 # use the proper spacing for first layer as we don't need to align
                 # its pattern to the other layers
-                $filler->set_spacing($base_flow->spacing);
+                $filler->set_min_spacing($base_flow->spacing);
             } else {
                 # draw a perimeter all around support infill
                 # TODO: use brim ordering algorithm
diff --git a/t/fill.t b/t/fill.t
index 7cea2726e5..a9e505c16e 100644
--- a/t/fill.t
+++ b/t/fill.t
@@ -30,7 +30,7 @@ sub scale_points (@) { map [scale $_->[X], scale $_->[Y]], @_ }
 {
     my $filler = Slic3r::Filler->new_from_type('rectilinear');
     $filler->set_angle(-(PI)/2);
-    $filler->set_spacing(5);
+    $filler->set_min_spacing(5);
     $filler->set_dont_adjust(1);
     $filler->set_endpoints_overlap(0);
     
@@ -44,7 +44,7 @@ sub scale_points (@) { map [scale $_->[X], scale $_->[Y]], @_ }
     };
     
     # square
-    $filler->set_density($filler->spacing / 50);
+    $filler->set_density($filler->min_spacing / 50);
     for my $i (0..3) {
         # check that it works regardless of the points order
         my @points = ([0,0], [100,0], [100,100], [0,100]);
@@ -64,7 +64,7 @@ sub scale_points (@) { map [scale $_->[X], scale $_->[Y]], @_ }
     # square with hole
     for my $angle (-(PI/2), -(PI/4), -(PI), PI/2, PI) {
         for my $spacing (25, 5, 7.5, 8.5) {
-            $filler->set_density($filler->spacing / $spacing);
+            $filler->set_density($filler->min_spacing / $spacing);
             $filler->set_angle($angle);
             my $paths = $test->(my $e = Slic3r::ExPolygon->new(
                 [ scale_points [0,0], [100,0], [100,100], [0,100] ],
@@ -102,7 +102,7 @@ sub scale_points (@) { map [scale $_->[X], scale $_->[Y]], @_ }
         height          => 0.4,
         nozzle_diameter => 0.50,
     );
-    $filler->set_spacing($flow->spacing);
+    $filler->set_min_spacing($flow->spacing);
     $filler->set_density(1);
     foreach my $angle (0, 45) {
         $surface->expolygon->rotate(Slic3r::Geometry::deg2rad($angle), [0,0]);
@@ -128,7 +128,7 @@ sub scale_points (@) { map [scale $_->[X], scale $_->[Y]], @_ }
             height          => 0.4,
             nozzle_diameter => $flow_spacing,
         );
-        $filler->set_spacing($flow->spacing);
+        $filler->set_min_spacing($flow->spacing);
         my $paths = $filler->fill_surface(
             $surface,
             layer_height    => $flow->height,
diff --git a/xs/src/libslic3r/Fill/Fill.cpp b/xs/src/libslic3r/Fill/Fill.cpp
index 82a392943e..c88a32514a 100644
--- a/xs/src/libslic3r/Fill/Fill.cpp
+++ b/xs/src/libslic3r/Fill/Fill.cpp
@@ -52,7 +52,10 @@ Fill::fill_surface(const Surface &surface)
     if (this->density == 0) return Polylines();
     
     // Perform offset.
-    ExPolygons expp = offset_ex(surface.expolygon, -scale_(this->spacing)/2);
+    ExPolygons expp = offset_ex(surface.expolygon, -scale_(this->min_spacing)/2);
+    
+    // Implementations can change this if they adjust the flow.
+    this->_spacing = this->min_spacing;
     
     // Create the infills for each of the regions.
     Polylines polylines_out;
@@ -85,6 +88,8 @@ Fill::adjust_solid_spacing(const coord_t width, const coord_t distance)
     assert(factor > 1. - 1e-5);
     
     // How much could the extrusion width be increased? By 20%.
+    // Because of this limit, this method is not idempotent: each run
+    // will increment distance by 20%.
     const coordf_t factor_max = 1.2;
     if (factor > factor_max)
         distance_new = floor((double)distance * factor_max + 0.5);
diff --git a/xs/src/libslic3r/Fill/Fill.hpp b/xs/src/libslic3r/Fill/Fill.hpp
index a733a870db..151d61436b 100644
--- a/xs/src/libslic3r/Fill/Fill.hpp
+++ b/xs/src/libslic3r/Fill/Fill.hpp
@@ -27,7 +27,7 @@ public:
     coordf_t    z;
     
     // in unscaled coordinates
-    coordf_t    spacing;
+    coordf_t    min_spacing;
     
     // overlap over spacing for extrusion endpoints
     float       endpoints_overlap;
@@ -78,11 +78,16 @@ public:
     // Perform the fill.
     virtual Polylines fill_surface(const Surface &surface);
     
+    coordf_t spacing() const { return this->_spacing; };
+    
 protected:
+    // the actual one in unscaled coordinates, we fill this while generating paths
+    coordf_t _spacing;
+    
     Fill() :
         layer_id(size_t(-1)),
         z(0.f),
-        spacing(0.f),
+        min_spacing(0.f),
         endpoints_overlap(0.3f),
         angle(0),
         link_max_length(0),
@@ -90,7 +95,8 @@ protected:
         density(0),
         dont_connect(false),
         dont_adjust(false),
-        complete(false)
+        complete(false),
+        _spacing(0.f)
         {};
     
     typedef std::pair<float, Point> direction_t;
diff --git a/xs/src/libslic3r/Fill/Fill3DHoneycomb.cpp b/xs/src/libslic3r/Fill/Fill3DHoneycomb.cpp
index 3f523b27c9..4464cc877f 100644
--- a/xs/src/libslic3r/Fill/Fill3DHoneycomb.cpp
+++ b/xs/src/libslic3r/Fill/Fill3DHoneycomb.cpp
@@ -156,7 +156,7 @@ Fill3DHoneycomb::_fill_surface_single(
 {
     // no rotation is supported for this infill pattern
     BoundingBox bb = expolygon.contour.bounding_box();
-    const coord_t distance = coord_t(scale_(this->spacing) / this->density);
+    const coord_t distance = coord_t(scale_(this->min_spacing) / this->density);
 
     // align bounding box to a multiple of our honeycomb grid module
     // (a module is 2*$distance since one $distance half-module is 
diff --git a/xs/src/libslic3r/Fill/FillConcentric.cpp b/xs/src/libslic3r/Fill/FillConcentric.cpp
index cb09993b9e..24d8f318a1 100644
--- a/xs/src/libslic3r/Fill/FillConcentric.cpp
+++ b/xs/src/libslic3r/Fill/FillConcentric.cpp
@@ -15,13 +15,13 @@ FillConcentric::_fill_surface_single(
 {
     // no rotation is supported for this infill pattern
     
-    const coord_t min_spacing = scale_(this->spacing);
+    const coord_t min_spacing = scale_(this->min_spacing);
     coord_t distance = coord_t(min_spacing / this->density);
     
     if (this->density > 0.9999f && !this->dont_adjust) {
         BoundingBox bounding_box = expolygon.contour.bounding_box();
         distance = this->adjust_solid_spacing(bounding_box.size().x, distance);
-        this->spacing = unscale(distance);
+        this->_spacing = unscale(distance);
     }
 
     Polygons loops = (Polygons)expolygon;
diff --git a/xs/src/libslic3r/Fill/FillHoneycomb.cpp b/xs/src/libslic3r/Fill/FillHoneycomb.cpp
index df4e62a3d1..02198bcd7d 100644
--- a/xs/src/libslic3r/Fill/FillHoneycomb.cpp
+++ b/xs/src/libslic3r/Fill/FillHoneycomb.cpp
@@ -14,12 +14,12 @@ FillHoneycomb::_fill_surface_single(
     Polylines*                      polylines_out)
 {
     // cache hexagons math
-    CacheID cache_id = std::make_pair(this->density, this->spacing);
+    CacheID cache_id = std::make_pair(this->density, this->min_spacing);
     Cache::iterator it_m = this->cache.find(cache_id);
     if (it_m == this->cache.end()) {
         it_m = this->cache.insert(it_m, std::pair<CacheID,CacheData>(cache_id, CacheData()));
         CacheData &m = it_m->second;
-        coord_t min_spacing = scale_(this->spacing);
+        coord_t min_spacing = scale_(this->min_spacing);
         m.distance          = min_spacing / this->density;
         m.hex_side          = m.distance / (sqrt(3)/2);
         m.hex_width         = m.distance * 2; // $m->{hex_width} == $m->{hex_side} * sqrt(3);
diff --git a/xs/src/libslic3r/Fill/FillPlanePath.cpp b/xs/src/libslic3r/Fill/FillPlanePath.cpp
index 09b0ea7000..2b78f24e15 100644
--- a/xs/src/libslic3r/Fill/FillPlanePath.cpp
+++ b/xs/src/libslic3r/Fill/FillPlanePath.cpp
@@ -14,7 +14,7 @@ void FillPlanePath::_fill_surface_single(
 {
     expolygon.rotate(-direction.first);
 
-    const coord_t distance_between_lines = scale_(this->spacing) / this->density;
+    const coord_t distance_between_lines = scale_(this->min_spacing) / this->density;
     
     // align infill across layers using the object's bounding box (if available)
     BoundingBox bounding_box = this->bounding_box.defined
diff --git a/xs/src/libslic3r/Fill/FillRectilinear.cpp b/xs/src/libslic3r/Fill/FillRectilinear.cpp
index 286b1a5506..9af1842958 100644
--- a/xs/src/libslic3r/Fill/FillRectilinear.cpp
+++ b/xs/src/libslic3r/Fill/FillRectilinear.cpp
@@ -22,7 +22,7 @@ FillRectilinear::_fill_single_direction(ExPolygon expolygon,
     expolygon.rotate(-direction.first);
     
     assert(this->density > 0.0001f && this->density <= 1.f);
-    const coord_t min_spacing   = scale_(this->spacing);
+    const coord_t min_spacing   = scale_(this->min_spacing);
     coord_t line_spacing        = (double) min_spacing / this->density;
     
     // We ignore this->bounding_box because it doesn't matter; we're doing align_to_grid below.
@@ -36,7 +36,7 @@ FillRectilinear::_fill_single_direction(ExPolygon expolygon,
     // define flow spacing according to requested density
     if (this->density > 0.9999f && !this->dont_adjust) {
         line_spacing = this->adjust_solid_spacing(bounding_box.size().x, line_spacing);
-        this->spacing = unscale(line_spacing);
+        this->_spacing = unscale(line_spacing);
     } else {
         // extend bounding box so that our pattern will be aligned with other layers
         // Transform the reference point to the rotated coordinate system.
@@ -451,7 +451,7 @@ void FillStars::_fill_surface_single(
     fill2._fill_single_direction(expolygon, direction2, 0, out);
     
     direction2.first += PI/3;
-    const coord_t x_shift = 0.5 * scale_(fill2.spacing) / fill2.density;
+    const coord_t x_shift = 0.5 * scale_(fill2.min_spacing) / fill2.density;
     fill2._fill_single_direction(expolygon, direction2, x_shift, out);
 }
 
@@ -465,7 +465,7 @@ void FillCubic::_fill_surface_single(
     fill2.density /= 3.;
     direction_t direction2 = direction;
     
-    const coord_t range = scale_(this->spacing / this->density);
+    const coord_t range = scale_(this->min_spacing / this->density);
     const coord_t x_shift = abs(( (coord_t)(scale_(this->z) + range) % (coord_t)(range * 2)) - range);
     
     fill2._fill_single_direction(expolygon, direction2, -x_shift, out);
diff --git a/xs/src/libslic3r/LayerRegionFill.cpp b/xs/src/libslic3r/LayerRegionFill.cpp
index 142e4758f0..6beb82e365 100644
--- a/xs/src/libslic3r/LayerRegionFill.cpp
+++ b/xs/src/libslic3r/LayerRegionFill.cpp
@@ -211,13 +211,14 @@ LayerRegion::make_fill()
                 -1,     // auto width
                 *this->layer()->object()
             );
-            f->spacing = internal_flow.spacing();
+            f->min_spacing = internal_flow.spacing();
             using_internal_flow = true;
         } else {
-            f->spacing = flow.spacing();
+            f->min_spacing = flow.spacing();
         }
+        
         f->endpoints_overlap = this->region()->config.get_abs_value("infill_overlap",
-            (perimeter_spacing + scale_(f->spacing))/2);
+            (perimeter_spacing + scale_(f->min_spacing))/2);
 
         f->layer_id = this->layer()->id();
         f->z        = this->layer()->print_z;
@@ -225,7 +226,7 @@ LayerRegion::make_fill()
         
         // Maximum length of the perimeter segment linking two infill lines.
         f->link_max_length = (!is_bridge && density > 80)
-            ? scale_(3 * f->spacing)
+            ? scale_(3 * f->min_spacing)
             : 0;
         
         // Used by the concentric infill pattern to clip the loops to create extrusion paths.
@@ -243,9 +244,9 @@ LayerRegion::make_fill()
         if (using_internal_flow) {
             // if we used the internal flow we're not doing a solid infill
             // so we can safely ignore the slight variation that might have
-            // been applied to f->spacing
+            // been applied to f->spacing()
         } else {
-            flow = Flow::new_from_spacing(f->spacing, flow.nozzle_diameter, h, is_bridge || f->use_bridge_flow());
+            flow = Flow::new_from_spacing(f->spacing(), flow.nozzle_diameter, h, is_bridge || f->use_bridge_flow());
         }
 
         // Save into layer.
diff --git a/xs/xsp/Filler.xsp b/xs/xsp/Filler.xsp
index 7a3e995d34..0c5c08b6c7 100644
--- a/xs/xsp/Filler.xsp
+++ b/xs/xsp/Filler.xsp
@@ -14,10 +14,13 @@
     void set_bounding_box(BoundingBox *bbox)
         %code{% THIS->fill->bounding_box = *bbox; %};
     
-    void set_spacing(coordf_t spacing)
-        %code{% THIS->fill->spacing = spacing; %};
+    void set_min_spacing(coordf_t spacing)
+        %code{% THIS->fill->min_spacing = spacing; %};
+    coordf_t min_spacing()
+        %code{% RETVAL = THIS->fill->min_spacing; %};
+    
     coordf_t spacing()
-        %code{% RETVAL = THIS->fill->spacing; %};
+        %code{% RETVAL = THIS->fill->spacing(); %};
     
     void set_endpoints_overlap(float overlap)
         %code{% THIS->fill->endpoints_overlap = overlap; %};