diff --git a/lib/Slic3r/Fill.pm b/lib/Slic3r/Fill.pm
index e30eec65..7d0556f8 100644
--- a/lib/Slic3r/Fill.pm
+++ b/lib/Slic3r/Fill.pm
@@ -170,7 +170,7 @@ sub make_fill {
                             ? ($surface->surface_type == S_TYPE_TOP ? EXTR_ROLE_TOPSOLIDFILL : EXTR_ROLE_SOLIDFILL)
                             : EXTR_ROLE_FILL),
                     depth_layers => $surface->depth_layers,
-                    flow_spacing => $params->{flow_spacing} || $flow_spacing,
+                    flow_spacing => $params->{flow_spacing} || (warn "Warning: no flow_spacing was returned by the infill engine, please report this to the developer\n"),
                 ), @paths,
             ],
         );
diff --git a/lib/Slic3r/Fill/Concentric.pm b/lib/Slic3r/Fill/Concentric.pm
index 94866e2a..c0d172cf 100644
--- a/lib/Slic3r/Fill/Concentric.pm
+++ b/lib/Slic3r/Fill/Concentric.pm
@@ -18,7 +18,7 @@ sub fill_surface {
     my $min_spacing = scale $params{flow_spacing};
     my $distance = $min_spacing / $params{density};
     
-    my $flow_spacing;
+    my $flow_spacing = $params{flow_spacing};
     if ($params{density} == 1) {
         $distance = $self->adjust_solid_spacing(
             width       => $bounding_box->[X2] - $bounding_box->[X1],
diff --git a/lib/Slic3r/Fill/Honeycomb.pm b/lib/Slic3r/Fill/Honeycomb.pm
index 229c7256..1e407e2e 100644
--- a/lib/Slic3r/Fill/Honeycomb.pm
+++ b/lib/Slic3r/Fill/Honeycomb.pm
@@ -94,7 +94,8 @@ sub fill_surface {
         paths => [ map Slic3r::ExtrusionPath->pack(polyline => $_, role => -1), @paths ],
     );
     
-    return {}, map $_->polyline, $collection->shortest_path;
+    return { flow_spacing => $params{flow_spacing} },
+        map $_->polyline, $collection->shortest_path;
 }
 
 1;
diff --git a/lib/Slic3r/Fill/PlanePath.pm b/lib/Slic3r/Fill/PlanePath.pm
index daeb13de..d33b6e6f 100644
--- a/lib/Slic3r/Fill/PlanePath.pm
+++ b/lib/Slic3r/Fill/PlanePath.pm
@@ -60,7 +60,7 @@ sub fill_surface {
     # paths must be rotated back
     $self->rotate_points_back(\@paths, $rotate_vector);
     
-    return {}, @paths;
+    return { flow_spacing => $params{flow_spacing} }, @paths;
 }
 
 1;
diff --git a/lib/Slic3r/Fill/Rectilinear.pm b/lib/Slic3r/Fill/Rectilinear.pm
index 2de7872a..bac965c1 100644
--- a/lib/Slic3r/Fill/Rectilinear.pm
+++ b/lib/Slic3r/Fill/Rectilinear.pm
@@ -22,7 +22,7 @@ sub fill_surface {
     my $distance_between_lines = $min_spacing / $params{density};
     my $line_oscillation = $distance_between_lines - $min_spacing;
     
-    my $flow_spacing;
+    my $flow_spacing = $params{flow_spacing};
     if ($params{density} == 1) {
         $distance_between_lines = $self->adjust_solid_spacing(
             width       => $bounding_box->[X2] - $bounding_box->[X1],