diff --git a/bugs_test.go b/bugs_test.go
index 1d1f727..0785b48 100644
--- a/bugs_test.go
+++ b/bugs_test.go
@@ -71,3 +71,18 @@ func TestBug3(t *T) {
 		t.Errorf("expected %s, got %s", exp, result)
 	}
 }
+
+// somewhat simplified variant, for easier debugging
+func TestBug3b(t *T) {
+	subject := polyclip.Polygon{{{1, 2}, {2, 2}, {2, 1}}}
+	clipping := polyclip.Polygon{
+		{{2, 1}, {2, 2}, {3, 2}},
+		{{1, 2}, {2, 3}, {2, 2}},
+		{{2, 2}, {2, 3}, {3, 2}}}
+	result := dump(subject.Construct(polyclip.UNION, clipping))
+
+	exp := dump(polyclip.Polygon{{{1, 2}, {2, 3}, {3, 2}, {2, 1}}})
+	if result != exp {
+		t.Errorf("expected %s, got %s", exp, result)
+	}
+}