diff --git a/lib/Slic3r/Layer/Region.pm b/lib/Slic3r/Layer/Region.pm
index 05713ba12..1cb7ae155 100644
--- a/lib/Slic3r/Layer/Region.pm
+++ b/lib/Slic3r/Layer/Region.pm
@@ -214,7 +214,7 @@ sub make_perimeters {
         
         # make sure we don't infill narrow parts that are already gap-filled
         # (we only consider this surface's gaps to reduce the diff() complexity)
-        @last = @{diff(\@last, \@last_gaps)};
+        @last = @{diff(\@last, [ map @$_, @last_gaps ])};
         
         # create one more offset to be used as boundary for fill
         # we offset by half the perimeter spacing (to get to the actual infill boundary)
@@ -508,7 +508,7 @@ sub process_external_surfaces {
 sub _detect_bridge_direction {
     my ($self, $expolygon, $lower_layer) = @_;
     
-    my $grown = $expolygon->offset_ex(+$self->perimeter_flow->scaled_width);
+    my $grown = $expolygon->offset(+$self->perimeter_flow->scaled_width);
     my @lower = @{$lower_layer->slices};       # expolygons
     
     # detect what edges lie on lower slices
@@ -516,7 +516,7 @@ sub _detect_bridge_direction {
     foreach my $lower (@lower) {
         # turn bridge contour and holes into polylines and then clip them
         # with each lower slice's contour
-        my @clipped = map $_->split_at_first_point->clip_with_polygon($lower->contour), map @$_, @$grown;
+        my @clipped = map $_->split_at_first_point->clip_with_polygon($lower->contour), @$grown;
         if (@clipped == 2) {
             # If the split_at_first_point() call above happens to split the polygon inside the clipping area
             # we would get two consecutive polylines instead of a single one, so we use this ugly hack to 
@@ -567,7 +567,7 @@ sub _detect_bridge_direction {
         
         # detect anchors as intersection between our bridge expolygon and the lower slices
         my $anchors = intersection_ex(
-            [ @$grown ],
+            $grown,
             [ map @$_, @lower ],
             1,  # safety offset required to avoid Clipper from detecting empty intersection while Boost actually found some @edges
         );
diff --git a/xs/src/ExPolygon.cpp b/xs/src/ExPolygon.cpp
index 7a58e969e..eaa209494 100644
--- a/xs/src/ExPolygon.cpp
+++ b/xs/src/ExPolygon.cpp
@@ -111,6 +111,8 @@ void
 ExPolygon::from_SV_check(SV* expoly_sv)
 {
     if (sv_isobject(expoly_sv) && (SvTYPE(SvRV(expoly_sv)) == SVt_PVMG)) {
+        if (!sv_isa(expoly_sv, "Slic3r::ExPolygon") && !sv_isa(expoly_sv, "Slic3r::ExPolygon::Ref"))
+            CONFESS("Not a valid Slic3r::ExPolygon object");
         // a XS ExPolygon was supplied
         *this = *(ExPolygon *)SvIV((SV*)SvRV( expoly_sv ));
     } else {
diff --git a/xs/src/Line.cpp b/xs/src/Line.cpp
index 0e4698b7f..31994a818 100644
--- a/xs/src/Line.cpp
+++ b/xs/src/Line.cpp
@@ -79,6 +79,8 @@ void
 Line::from_SV_check(SV* line_sv)
 {
     if (sv_isobject(line_sv) && (SvTYPE(SvRV(line_sv)) == SVt_PVMG)) {
+        if (!sv_isa(line_sv, "Slic3r::Line") && !sv_isa(line_sv, "Slic3r::Line::Ref"))
+            CONFESS("Not a valid Slic3r::Line object");
         *this = *(Line*)SvIV((SV*)SvRV( line_sv ));
     } else {
         this->from_SV(line_sv);
diff --git a/xs/src/Point.cpp b/xs/src/Point.cpp
index b39a06c11..9251eca93 100644
--- a/xs/src/Point.cpp
+++ b/xs/src/Point.cpp
@@ -122,6 +122,8 @@ void
 Point::from_SV_check(SV* point_sv)
 {
     if (sv_isobject(point_sv) && (SvTYPE(SvRV(point_sv)) == SVt_PVMG)) {
+        if (!sv_isa(point_sv, "Slic3r::Point") && !sv_isa(point_sv, "Slic3r::Point::Ref"))
+            CONFESS("Not a valid Slic3r::Point object");
         *this = *(Point*)SvIV((SV*)SvRV( point_sv ));
     } else {
         this->from_SV(point_sv);
diff --git a/xs/src/Polygon.cpp b/xs/src/Polygon.cpp
index 592503e2e..e7fa7a6ef 100644
--- a/xs/src/Polygon.cpp
+++ b/xs/src/Polygon.cpp
@@ -126,6 +126,15 @@ Polygon::to_SV_clone_ref() const {
     sv_setref_pv( sv, "Slic3r::Polygon", new Polygon(*this) );
     return sv;
 }
+
+void
+Polygon::from_SV_check(SV* poly_sv)
+{
+    if (sv_isobject(poly_sv) && !sv_isa(poly_sv, "Slic3r::Polygon") && !sv_isa(poly_sv, "Slic3r::Polygon::Ref"))
+        CONFESS("Not a valid Slic3r::Polygon object");
+    
+    MultiPoint::from_SV_check(poly_sv);
+}
 #endif
 
 }
diff --git a/xs/src/Polygon.hpp b/xs/src/Polygon.hpp
index ab04ed624..d31f3c4ff 100644
--- a/xs/src/Polygon.hpp
+++ b/xs/src/Polygon.hpp
@@ -25,6 +25,7 @@ class Polygon : public MultiPoint {
     bool is_valid() const;
     
     #ifdef SLIC3RXS
+    void from_SV_check(SV* poly_sv);
     SV* to_SV_ref();
     SV* to_SV_clone_ref() const;
     #endif
diff --git a/xs/src/Polyline.cpp b/xs/src/Polyline.cpp
index fc3950757..e7b65eb5f 100644
--- a/xs/src/Polyline.cpp
+++ b/xs/src/Polyline.cpp
@@ -96,6 +96,15 @@ Polyline::to_SV_clone_ref() const
     sv_setref_pv( sv, "Slic3r::Polyline", new Polyline(*this) );
     return sv;
 }
+
+void
+Polyline::from_SV_check(SV* poly_sv)
+{
+    if (!sv_isa(poly_sv, "Slic3r::Polyline") && !sv_isa(poly_sv, "Slic3r::Polyline::Ref"))
+        CONFESS("Not a valid Slic3r::Polyline object");
+    
+    MultiPoint::from_SV_check(poly_sv);
+}
 #endif
 
 }
diff --git a/xs/src/Polyline.hpp b/xs/src/Polyline.hpp
index c17b97f9f..b7401bad4 100644
--- a/xs/src/Polyline.hpp
+++ b/xs/src/Polyline.hpp
@@ -15,6 +15,7 @@ class Polyline : public MultiPoint {
     Points equally_spaced_points(double distance) const;
     
     #ifdef SLIC3RXS
+    void from_SV_check(SV* poly_sv);
     SV* to_SV_ref();
     SV* to_SV_clone_ref() const;
     #endif