diff --git a/t/fill.t b/t/fill.t
index 7da926d43..9cbd8c940 100644
--- a/t/fill.t
+++ b/t/fill.t
@@ -275,6 +275,7 @@ for my $pattern (qw(rectilinear honeycomb hilbertcurve concentric)) {
     $config->set('nozzle_diameter', [0.35]);
     $config->set('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);
     
     my $print = Slic3r::Test::init_print('A', config => $config);
@@ -299,7 +300,7 @@ 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 $_->area >= 4*($grow_d**2), @{diff_ex($layer0_infill, $layer1_infill)} ];
+    my $diff = [ grep { $_->area > 2*(($grow_d*2)**2) } @{diff_ex($layer0_infill, $layer1_infill)} ];
     is scalar(@$diff), 0, 'no missing parts in solid shell when fill_density is 0';
 }
 
diff --git a/t/perimeters.t b/t/perimeters.t
index 88b6b0a9e..17e1b31c7 100644
--- a/t/perimeters.t
+++ b/t/perimeters.t
@@ -186,12 +186,13 @@ use Slic3r::Test;
     
     # compute the covered area
     my $pflow = $layerm->flow(FLOW_ROLE_PERIMETER);
+    my $iflow = $layerm->flow(FLOW_ROLE_INFILL);
     my $covered_by_perimeters = union_ex([
         (map @{$_->polygon->split_at_first_point->grow($pflow->scaled_width/2)}, @{$layerm->perimeters}),
     ]);
     my $covered_by_infill = union_ex([
         (map $_->p, @{$layerm->fill_surfaces}),
-        (map @{$_->polyline->grow($pflow->scaled_width/2)}, @{$layerm->thin_fills}),
+        (map @{$_->polyline->grow($iflow->scaled_width/2)}, @{$layerm->thin_fills}),
     ]);
     
     # compute the non covered area
@@ -211,7 +212,7 @@ use Slic3r::Test;
         );
     }
     
-    ok !(defined first { $_->area > ($pflow->scaled_width**2) } @$non_covered), 'no gap between perimeters and infill';
+    ok !(defined first { $_->area > ($iflow->scaled_width**2) } @$non_covered), 'no gap between perimeters and infill';
 }
 
 {
diff --git a/xs/src/Flow.cpp b/xs/src/Flow.cpp
index 00c6cdc9c..1592e0c35 100644
--- a/xs/src/Flow.cpp
+++ b/xs/src/Flow.cpp
@@ -43,14 +43,8 @@ Flow::spacing() const {
         return this->width + BRIDGE_EXTRA_SPACING;
     }
     
-    float min_flow_spacing;
-    if (this->width >= (this->nozzle_diameter + this->height)) {
-        // rectangle with semicircles at the ends
-        min_flow_spacing = this->width - this->height * (1 - PI/4.0);
-    } else {
-        // rectangle with shrunk semicircles at the ends
-        min_flow_spacing = this->nozzle_diameter * (1 - PI/4.0) + this->width * PI/4.0;
-    }
+    // rectangle with semicircles at the ends
+    float min_flow_spacing = this->width - this->height * (1 - PI/4.0);
     return this->width - OVERLAP_FACTOR * (this->width - min_flow_spacing);
 }
 
@@ -74,13 +68,10 @@ double
 Flow::mm3_per_mm() const {
     if (this->bridge) {
         return (this->width * this->width) * PI/4.0;
-    } else if (this->width >= (this->nozzle_diameter + this->height)) {
-        // rectangle with semicircles at the ends
-        return this->width * this->height + (this->height*this->height) / 4.0 * (PI-4.0);
-    } else {
-        // rectangle with shrunk semicircles at the ends
-        return this->nozzle_diameter * this->height * (1 - PI/4.0) + this->height * this->width * PI/4.0;
     }
+    
+    // rectangle with semicircles at the ends
+    return this->width * this->height + (this->height*this->height) / 4.0 * (PI-4.0);
 }
 
 /* This static method returns bridge width for a given nozzle diameter. */
@@ -94,16 +85,8 @@ Flow::_bridge_width(float nozzle_diameter, float bridge_flow_ratio) {
 float
 Flow::_auto_width(FlowRole role, float nozzle_diameter, float height) {
     // here we calculate a sane default by matching the flow speed (at the nozzle) and the feed rate
-    float volume = (nozzle_diameter*nozzle_diameter) * PI/4.0;
-    float shape_threshold = nozzle_diameter * height + (height*height) * PI/4.0;
-    float width;
-    if (volume >= shape_threshold) {
-        // rectangle with semicircles at the ends
-        width = ((nozzle_diameter*nozzle_diameter) * PI + (height*height) * (4.0 - PI)) / (4.0 * height);
-    } else {
-        // rectangle with squished semicircles at the ends
-        width = nozzle_diameter * (nozzle_diameter/height - 4.0/PI + 1);
-    }
+    // shape: rectangle with semicircles at the ends
+    float width = ((nozzle_diameter*nozzle_diameter) * PI + (height*height) * (4.0 - PI)) / (4.0 * height);
     
     float min = nozzle_diameter * 1.05;
     float max = -1;
@@ -126,16 +109,8 @@ Flow::_width_from_spacing(float spacing, float nozzle_diameter, float height, bo
         return spacing - BRIDGE_EXTRA_SPACING;
     }
     
-    float w_threshold = height + nozzle_diameter;
-    float s_threshold = w_threshold - OVERLAP_FACTOR * (w_threshold - (w_threshold - height * (1 - PI/4.0)));
-    
-    if (spacing >= s_threshold) {
-        // rectangle with semicircles at the ends
-        return spacing + OVERLAP_FACTOR * height * (1 - PI/4.0);
-    } else {
-        // rectangle with shrunk semicircles at the ends
-        return (spacing + nozzle_diameter * OVERLAP_FACTOR * (PI/4.0 - 1)) / (1 + OVERLAP_FACTOR * (PI/4.0 - 1));
-    }
+    // rectangle with semicircles at the ends
+    return spacing + OVERLAP_FACTOR * height * (1 - PI/4.0);
 }
 
 #ifdef SLIC3RXS