diff --git a/lib/Slic3r/Fill.pm b/lib/Slic3r/Fill.pm
index 968b27f61..c22b9186c 100644
--- a/lib/Slic3r/Fill.pm
+++ b/lib/Slic3r/Fill.pm
@@ -182,11 +182,9 @@ sub make_fill {
         next if $surface->surface_type == S_TYPE_INTERNALVOID;
         my $filler          = $layerm->config->fill_pattern;
         my $density         = $fill_density;
-        my $flow            = ($surface->surface_type == S_TYPE_TOP)
-            ? $layerm->flow(FLOW_ROLE_TOP_SOLID_INFILL)
-            : $surface->is_solid
-                ? $solid_infill_flow
-                : $infill_flow;
+        my $role = ($surface->surface_type == S_TYPE_TOP) ? FLOW_ROLE_TOP_SOLID_INFILL
+            : $surface->is_solid ? FLOW_ROLE_SOLID_INFILL
+            : FLOW_ROLE_INFILL;
         my $is_bridge       = $layerm->id > 0 && $surface->is_bridge;
         my $is_solid        = $surface->is_solid;
         
@@ -196,7 +194,6 @@ sub make_fill {
             $filler = $layerm->config->solid_fill_pattern;
             if ($is_bridge) {
                 $filler = 'rectilinear';
-                $flow = $layerm->flow(FLOW_ROLE_SOLID_INFILL, 1);
             } elsif ($surface->surface_type == S_TYPE_INTERNALSOLID) {
                 $filler = 'rectilinear';
             }
@@ -204,19 +201,26 @@ sub make_fill {
             next SURFACE unless $density > 0;
         }
         
+        my $h = $surface->thickness == -1 ? $layerm->height : $surface->thickness;
+        my $flow = $layerm->region->flow(
+            $role,
+            $h,
+            $is_bridge,
+            $layerm->id == 0,
+        );
+        
         my $f = $self->filler($filler);
         $f->layer_id($layerm->id);
         $f->angle($layerm->config->fill_angle);
         my ($params, @polylines) = $f->fill_surface(
             $surface,
-            density => $density/100,
-            flow    => $flow,
+            density         => $density/100,
+            flow            => $flow,
+            layer_height    => $h,
         );
         next unless @polylines;
         
-        my $h = $surface->thickness;
-        $h = $layerm->height if $h == -1;
-        my $mm3_per_mm = $params->{flow}->mm3_per_mm($h);
+        my $mm3_per_mm = $flow->mm3_per_mm($h);
         
         # save into layer
         push @fills, my $collection = Slic3r::ExtrusionPath::Collection->new;
diff --git a/lib/Slic3r/Fill/Rectilinear.pm b/lib/Slic3r/Fill/Rectilinear.pm
index d8ba2870e..15b936131 100644
--- a/lib/Slic3r/Fill/Rectilinear.pm
+++ b/lib/Slic3r/Fill/Rectilinear.pm
@@ -33,7 +33,7 @@ sub fill_surface {
         $flow = Slic3r::Flow->new_from_spacing(
             spacing             => unscale($line_spacing),
             nozzle_diameter     => $flow->nozzle_diameter,
-            layer_height        => $surface->thickness,
+            layer_height        => ($params{layer_height} or die "No layer_height supplied to fill_surface()"),
             bridge              => $flow->bridge,
         );
     } else {
diff --git a/lib/Slic3r/Print/SupportMaterial.pm b/lib/Slic3r/Print/SupportMaterial.pm
index 712d09ab0..864d26824 100644
--- a/lib/Slic3r/Print/SupportMaterial.pm
+++ b/lib/Slic3r/Print/SupportMaterial.pm
@@ -552,6 +552,7 @@ sub generate_toolpaths {
                     Slic3r::Surface->new(expolygon => $expolygon, surface_type => S_TYPE_INTERNAL),
                     density     => $interface_density,
                     flow        => $interface_flow,
+                    layer_height => $layer->height,
                     complete    => 1,
                 );
                 my $mm3_per_mm = $params->{flow}->mm3_per_mm($layer->height);
@@ -602,6 +603,7 @@ sub generate_toolpaths {
                     Slic3r::Surface->new(expolygon => $expolygon, surface_type => S_TYPE_INTERNAL),
                     density     => $density,
                     flow        => $base_flow,
+                    layer_height => $layer->height,
                     complete    => 1,
                 );
                 my $mm3_per_mm = $params->{flow}->mm3_per_mm($layer->height);
diff --git a/t/fill.t b/t/fill.t
index 365d8e062..1192f81e2 100644
--- a/t/fill.t
+++ b/t/fill.t
@@ -51,7 +51,7 @@ sub scale_points (@) { map [scale $_->[X], scale $_->[Y]], @_ }
     );
     foreach my $angle (0, 45) {
         $surface->expolygon->rotate(Slic3r::Geometry::deg2rad($angle), [0,0]);
-        my ($params, @paths) = $filler->fill_surface($surface, flow => $flow, density => 0.4);
+        my ($params, @paths) = $filler->fill_surface($surface, flow => $flow, layer_height => 0.4, density => 0.4);
         is scalar @paths, 1, 'one continuous path';
     }
 }
@@ -76,6 +76,7 @@ sub scale_points (@) { map [scale $_->[X], scale $_->[Y]], @_ }
         my ($params, @paths) = $filler->fill_surface(
             $surface,
             flow            => $flow,
+            layer_height    => 0.4,
             density         => $density // 1,
         );
         
diff --git a/xs/src/Flow.cpp b/xs/src/Flow.cpp
index e5e7dc2be..13c12bef6 100644
--- a/xs/src/Flow.cpp
+++ b/xs/src/Flow.cpp
@@ -5,6 +5,9 @@ namespace Slic3r {
 
 Flow
 Flow::new_from_config_width(FlowRole role, const ConfigOptionFloatOrPercent &width, float nozzle_diameter, float height, float bridge_flow_ratio) {
+    // we need layer height unless it's a bridge
+    if (height <= 0 && bridge_flow_ratio == 0) CONFESS("Invalid flow height supplied to new_from_config_width()");
+    
     float w;
     if (!width.percent && width.value == 0) {
         w = Flow::_width(role, nozzle_diameter, height, bridge_flow_ratio);
@@ -19,6 +22,9 @@ Flow::new_from_config_width(FlowRole role, const ConfigOptionFloatOrPercent &wid
 
 Flow
 Flow::new_from_spacing(float spacing, float nozzle_diameter, float height, bool bridge) {
+    // we need layer height unless it's a bridge
+    if (height <= 0 && !bridge) CONFESS("Invalid flow height supplied to new_from_spacing()");
+
     float w = Flow::_width_from_spacing(spacing, nozzle_diameter, height, bridge);
     Flow flow(w, spacing, nozzle_diameter);
     flow.bridge = bridge;