diff --git a/src/libslic3r/MedialAxis.cpp b/src/libslic3r/MedialAxis.cpp
index 364f039b8..41f44171e 100644
--- a/src/libslic3r/MedialAxis.cpp
+++ b/src/libslic3r/MedialAxis.cpp
@@ -1149,7 +1149,7 @@ MedialAxis::concatenate_polylines_with_crossing(ThickPolylines& pp)
             Vec2d v_other(other_reverse ? other.lines().back().vector().x() : other.lines().front().vector().x(),
                 other_reverse ? other.lines().back().vector().y() : other.lines().front().vector().y());
             v_other *= (1 / std::sqrt(v_other.x()*v_other.x() + v_other.y()*v_other.y()));
-            float other_dot = (float)( v_poly.x()*v_other.x() + v_poly.y()*v_other.y() );
+            float other_dot = std::abs(float( v_poly.x()*v_other.x() + v_poly.y()*v_other.y() ));
             if (other_dot > best_dot) {
                 best_candidate = &other;
                 best_idx = j;
diff --git a/src/libslic3r/PerimeterGenerator.cpp b/src/libslic3r/PerimeterGenerator.cpp
index 7993b88da..400a78e1e 100644
--- a/src/libslic3r/PerimeterGenerator.cpp
+++ b/src/libslic3r/PerimeterGenerator.cpp
@@ -50,6 +50,9 @@ void PerimeterGenerator::process()
     
     // solid infill
     coord_t solid_infill_spacing    = this->solid_infill_flow.scaled_spacing();
+
+    // nozzle diameter
+    const double nozzle_diameter = this->print_config->nozzle_diameter.get_at(this->config->perimeter_extruder - 1);
     
     // Calculate the minimum required spacing between two adjacent traces.
     // This should be equal to the nominal flow spacing but we experiment
@@ -69,7 +72,6 @@ void PerimeterGenerator::process()
         // We consider overhang any part where the entire nozzle diameter is not supported by the
         // lower layer, so we take lower slices and offset them by half the nozzle diameter used 
         // in the current layer
-        double nozzle_diameter = this->print_config->nozzle_diameter.get_at(this->config->perimeter_extruder-1);
         this->_lower_slices_p = offset(*this->lower_slices, double(scale_(+nozzle_diameter/2)));
     }
     
@@ -587,6 +589,8 @@ void PerimeterGenerator::process()
         if (!gaps.empty()) {
             // collapse 
             double min = 0.2 * perimeter_width * (1 - INSET_OVERLAP_TOLERANCE);
+            //be sure we don't gapfill where the perimeters are already touching each other (negative spacing).
+            min = std::max(min, double(Flow::new_from_spacing(EPSILON, nozzle_diameter, this->layer_height, false).scaled_width()));
             double max = 2. * perimeter_spacing;
             ExPolygons gaps_ex = diff_ex(
                 offset2_ex(gaps, double(-min / 2), double(+min / 2)),