diff --git a/lib/Slic3r/AdaptiveSlicing.pm b/lib/Slic3r/AdaptiveSlicing.pm
index da624edac..8bd989585 100644
--- a/lib/Slic3r/AdaptiveSlicing.pm
+++ b/lib/Slic3r/AdaptiveSlicing.pm
@@ -177,7 +177,7 @@ sub horizontal_facet_distance {
 		# min_z == max_z -> horizontal facet
 		if($self->ordered_facets->[$ordered_id]->[1] > $z) {
 			if($self->ordered_facets->[$ordered_id]->[1] == $self->ordered_facets->[$ordered_id]->[2]) {
-				return unscale $self->ordered_facets->[$ordered_id]->[1] - $z;
+				return unscale($self->ordered_facets->[$ordered_id]->[1] - $z);
 			}
 		}
 		
@@ -185,11 +185,11 @@ sub horizontal_facet_distance {
 	}
 	
 	# objects maximum?
-	if($z + $max_height > $self->size) {
-		return 	max(unscale $self->size - $z, 0);
+	if($z + $max_height > scale($self->size)) {
+		return 	max($self->size - unscale($z), 0);
 	}
+
 	return unscale $max_height;
 }
 
-
 1;
\ No newline at end of file
diff --git a/t/adaptive_slicing.t b/t/adaptive_slicing.t
index 95c7df4e0..59354951b 100644
--- a/t/adaptive_slicing.t
+++ b/t/adaptive_slicing.t
@@ -1,4 +1,4 @@
-use Test::More tests => 5;
+use Test::More tests => 8;
 use strict;
 use warnings;
 
@@ -84,4 +84,38 @@ ok  (_eq($adaptive_slicing->cusp_height(scale 2.798, 0.1, 0.1, 0.5), 0.1414), 'r
 # slopes cusp height must be smaller than the distance to the slope
 ok  (_eq($adaptive_slicing->cusp_height(scale 2.6289, 0.15, 0.1, 0.5), 0.3), 'reducing cusp_height to z-diff');
 
+subtest 'horizontal planes' => sub {
+    plan tests => 3;
+
+	print "facet_distance: " . $adaptive_slicing->horizontal_facet_distance(scale 1, 1.2) . "\n";
+	ok  (_eq($adaptive_slicing->horizontal_facet_distance(scale 1, 1.2), 1.2), 'max_height limit');
+	ok  (_eq($adaptive_slicing->horizontal_facet_distance(scale 8.5, 4), 1.5), 'normal horizontal facet');
+	ok  (_eq($adaptive_slicing->horizontal_facet_distance(scale 17, 5), 3.0), 'object maximum');
+};
+
+# shrink current layer to fit another layer under horizontal facet
+$config->set('start_gcode', '');  # to avoid dealing with the nozzle lift in start G-code
+$config->set('z_offset', 0);
+
+$config->set('adaptive_slicing', 1);
+$config->set('first_layer_height', 0.42893); # to catch lower slope edge
+$config->set('nozzle_diameter', [0.5]);
+$config->set('min_layer_height', [0.1]);
+$config->set('max_layer_height', [0.5]);
+$config->set('cusp_value', [0.19]);
+# slope height: 7,07107 (2.92893 to 10)
+
+subtest 'shrink to match horizontal facets' => sub {
+	plan tests => 3;
+	$test->();
+};
+	
+# widen current layer to match horizontal facet
+$config->set('cusp_value', [0.1]);
+
+subtest 'widen to match horizontal facets' => sub {
+	plan tests => 3;
+	$test->();
+};
+
 __END__