diff --git a/lib/Slic3r/Config.pm b/lib/Slic3r/Config.pm
index 41cdd72a7a..e6132af099 100644
--- a/lib/Slic3r/Config.pm
+++ b/lib/Slic3r/Config.pm
@@ -646,7 +646,7 @@ sub validate {
     # calculate flow
     $Slic3r::flow->calculate($Slic3r::extrusion_width);
     if ($Slic3r::first_layer_extrusion_width) {
-        $Slic3r::first_layer_flow = Slic3r::Flow->new;
+        $Slic3r::first_layer_flow = Slic3r::Flow->new(layer_height => $Slic3r::_first_layer_height);
         $Slic3r::first_layer_flow->calculate($Slic3r::first_layer_extrusion_width);
     }
     $Slic3r::perimeters_flow->calculate($Slic3r::perimeters_extrusion_width || $Slic3r::extrusion_width);
diff --git a/lib/Slic3r/Flow.pm b/lib/Slic3r/Flow.pm
index 6a5675c3a5..4fe37bcbc5 100644
--- a/lib/Slic3r/Flow.pm
+++ b/lib/Slic3r/Flow.pm
@@ -3,9 +3,12 @@ use Moo;
 
 use Slic3r::Geometry qw(PI);
 
-has 'width' => (is => 'rw');
-has 'min_spacing' => (is => 'rw');
-has 'spacing' => (is => 'rw');
+has 'width'         => (is => 'rw');
+has 'min_spacing'   => (is => 'rw');
+has 'spacing'       => (is => 'rw');
+has 'layer_height'  => (is => 'lazy', builder => 1);
+
+sub _build_layer_height { $Slic3r::layer_height }
 
 sub calculate {
     my $self = shift;
@@ -14,20 +17,20 @@ sub calculate {
     my ($flow_width, $min_flow_spacing, $flow_spacing);
     if ($extrusion_width) {
         $flow_width = $extrusion_width =~ /^(\d+(?:\.\d+)?)%$/
-            ? ($Slic3r::layer_height * $1 / 100)
+            ? ($self->layer_height * $1 / 100)
             : $extrusion_width;
     } else {
         # here we calculate a sane default by matching the flow speed (at the nozzle)
         # and the feed rate
         my $volume = ($Slic3r::nozzle_diameter**2) * PI/4;
-        my $shape_threshold = $Slic3r::nozzle_diameter * $Slic3r::layer_height
-            + ($Slic3r::layer_height**2) * PI/4;
+        my $shape_threshold = $Slic3r::nozzle_diameter * $self->layer_height
+            + ($self->layer_height**2) * PI/4;
         if ($volume >= $shape_threshold) {
             # rectangle with semicircles at the ends
-            $flow_width = (($Slic3r::nozzle_diameter**2) * PI + ($Slic3r::layer_height**2) * (4 - PI)) / (4 * $Slic3r::layer_height);
+            $flow_width = (($Slic3r::nozzle_diameter**2) * PI + ($self->layer_height**2) * (4 - PI)) / (4 * $self->layer_height);
         } else {
             # rectangle with squished semicircles at the ends
-            $flow_width = $Slic3r::nozzle_diameter * ($Slic3r::nozzle_diameter/$Slic3r::layer_height - 4/PI + 1);
+            $flow_width = $Slic3r::nozzle_diameter * ($Slic3r::nozzle_diameter/$self->layer_height - 4/PI + 1);
         }
         
         my $min_flow_width = $Slic3r::nozzle_diameter * 1.05;
@@ -36,9 +39,9 @@ sub calculate {
         $flow_width = $min_flow_width if $flow_width < $min_flow_width;
     }
     
-    if ($flow_width >= ($Slic3r::nozzle_diameter + $Slic3r::layer_height)) {
+    if ($flow_width >= ($Slic3r::nozzle_diameter + $self->layer_height)) {
         # rectangle with semicircles at the ends
-        $min_flow_spacing = $flow_width - $Slic3r::layer_height * (1 - PI/4);
+        $min_flow_spacing = $flow_width - $self->layer_height * (1 - PI/4);
     } else {
         # rectangle with shrunk semicircles at the ends
         $min_flow_spacing = $flow_width * (1 - PI/4) + $Slic3r::nozzle_diameter * PI/4;