diff --git a/lib/Slic3r/Fill.pm b/lib/Slic3r/Fill.pm
index 85c189cfec..1a76c6a670 100644
--- a/lib/Slic3r/Fill.pm
+++ b/lib/Slic3r/Fill.pm
@@ -13,7 +13,7 @@ use Slic3r::Fill::PlanePath;
 use Slic3r::Fill::Rectilinear;
 use Slic3r::ExtrusionPath ':roles';
 use Slic3r::Geometry qw(X Y PI scale chained_path);
-use Slic3r::Geometry::Clipper qw(union_ex diff_ex);
+use Slic3r::Geometry::Clipper qw(union_ex diff_ex intersection_ex offset);
 use Slic3r::Surface ':types';
 
 
@@ -98,15 +98,40 @@ sub make_fill {
         }
     }
     
-    # add spacing between surfaces
+    # we need to detect any narrow surfaces that might collapse
+    # when adding spacing below
+    # such narrow surfaces are often generated in sloping walls
+    # by bridge_over_infill() and combine_infill() as a result of the
+    # subtraction of the combinable area from the layer infill area,
+    # which leaves small areas near the perimeters
+    # we are going to grow such regions by overlapping them with the void (if any)
+    # TODO: detect and investigate whether there could be narrow regions without
+    # any void neighbors
+    my $distance_between_surfaces = $layerm->infill_flow->scaled_spacing;
     {
-        my $distance = $layerm->infill_flow->scaled_spacing / 2;
-        @surfaces = map $_->offset(-$distance), @surfaces;
+        my $collapsed = diff_ex(
+            [ map @{$_->expolygon}, @surfaces ],
+            [ offset(
+                [ offset([ map @{$_->expolygon}, @surfaces ], -$distance_between_surfaces/2) ],
+                +$distance_between_surfaces/2
+            ) ],
+        );
+        push @surfaces, map Slic3r::Surface->new(
+            expolygon       => $_,
+            surface_type    => S_TYPE_INTERNALSOLID,
+        ), @{intersection_ex(
+            [ offset([ map @$_, @$collapsed ], $distance_between_surfaces) ],
+            [ map @{$_->expolygon}, grep $_->surface_type == S_TYPE_INTERNALVOID, @surfaces ],
+        )};
     }
     
+    # add spacing between surfaces
+    @surfaces = map $_->offset(-$distance_between_surfaces/2), @surfaces;
+    
     my @fills = ();
     my @fills_ordering_points =  ();
     SURFACE: foreach my $surface (@surfaces) {
+        next if $surface->surface_type == S_TYPE_INTERNALVOID;
         my $filler          = $Slic3r::Config->fill_pattern;
         my $density         = $Slic3r::Config->fill_density;
         my $flow_spacing    = ($surface->surface_type == S_TYPE_TOP)
diff --git a/lib/Slic3r/Print/Object.pm b/lib/Slic3r/Print/Object.pm
index 6008e02ebf..3e4c1fafc1 100644
--- a/lib/Slic3r/Print/Object.pm
+++ b/lib/Slic3r/Print/Object.pm
@@ -516,6 +516,13 @@ sub bridge_over_infill {
                                 [ map $_->p, @$group ],
                                 [ map @$_, @$to_bridge ],
                             )};
+                            push @new_surfaces, map Slic3r::Surface->new(
+                                expolygon       => $_,
+                                surface_type    => S_TYPE_INTERNALVOID,
+                            ), @{intersection_ex(
+                                [ map $_->p, @$group ],
+                                [ map @$_, @$to_bridge ],
+                            )};
                         }
                         @{$lower_layerm->fill_surfaces} = @new_surfaces;
                     }
@@ -713,7 +720,7 @@ sub combine_infill {
                     my @this_type   = grep $_->surface_type == $type, @{$layerm->fill_surfaces};
                     my @other_types = grep $_->surface_type != $type, @{$layerm->fill_surfaces};
                     
-                    @this_type = map Slic3r::Surface->new(expolygon => $_, surface_type => $type),
+                    my @new_this_type = map Slic3r::Surface->new(expolygon => $_, surface_type => $type),
                         @{diff_ex(
                             [ map @{$_->expolygon}, @this_type ],
                             [ @intersection_with_clearance ],
@@ -721,12 +728,20 @@ sub combine_infill {
                     
                     # apply surfaces back with adjusted depth to the uppermost layer
                     if ($layerm->id == $layer_id) {
-                        push @this_type,
+                        push @new_this_type,
                             map Slic3r::Surface->new(expolygon => $_, surface_type => $type, depth_layers => $every),
                             @$intersection;
+                    } else {
+                        # save void surfaces
+                        push @this_type,
+                            map Slic3r::Surface->new(expolygon => $_, surface_type => S_TYPE_INTERNALVOID),
+                            @{intersection_ex(
+                                [ map @{$_->expolygon}, @this_type ],
+                                [ @intersection_with_clearance ],
+                            )};
                     }
                     
-                    @{$layerm->fill_surfaces} = (@this_type, @other_types);
+                    @{$layerm->fill_surfaces} = (@new_this_type, @other_types);
                 }
             }
         }
diff --git a/lib/Slic3r/Surface.pm b/lib/Slic3r/Surface.pm
index efa0f46a99..cb8aab3130 100644
--- a/lib/Slic3r/Surface.pm
+++ b/lib/Slic3r/Surface.pm
@@ -4,7 +4,7 @@ use warnings;
 
 require Exporter;
 our @ISA = qw(Exporter);
-our @EXPORT_OK   = qw(S_TYPE_TOP S_TYPE_BOTTOM S_TYPE_INTERNAL S_TYPE_INTERNALSOLID S_TYPE_INTERNALBRIDGE);
+our @EXPORT_OK   = qw(S_TYPE_TOP S_TYPE_BOTTOM S_TYPE_INTERNAL S_TYPE_INTERNALSOLID S_TYPE_INTERNALBRIDGE S_TYPE_INTERNALVOID);
 our %EXPORT_TAGS = (types => \@EXPORT_OK);
 
 use constant S_EXPOLYGON    => 0;
@@ -18,6 +18,7 @@ use constant S_TYPE_BOTTOM          => 1;
 use constant S_TYPE_INTERNAL        => 2;
 use constant S_TYPE_INTERNALSOLID   => 3;
 use constant S_TYPE_INTERNALBRIDGE  => 4;
+use constant S_TYPE_INTERNALVOID    => 5;
 
 sub new {
     my $class = shift;
@@ -74,17 +75,6 @@ sub offset {
     } $self->expolygon->offset_ex(@_);
 }
 
-sub clipper_polygon {
-    my $self = shift;
-    
-    return {
-        outer => $self->contour->p,
-        holes => [
-            map $_->p, @{$self->holes}
-        ],
-    };
-}
-
 sub p {
     my $self = shift;
     return @{$self->expolygon};
@@ -99,14 +89,6 @@ sub is_solid {
         || $type == S_TYPE_INTERNALSOLID;
 }
 
-sub is_internal {
-    my $self = shift;
-    my $type = $self->surface_type;
-    return $type == S_TYPE_INTERNAL
-        || $type == S_TYPE_INTERNALSOLID
-        || $type == S_TYPE_INTERNALBRIDGE;
-}
-
 sub is_bridge {
     my $self = shift;
     my $type = $self->surface_type;