diff --git a/poly2d/cgal_helper.h b/poly2d/cgal_helper.h
index 8e6886f..8c649e0 100644
--- a/poly2d/cgal_helper.h
+++ b/poly2d/cgal_helper.h
@@ -1,8 +1,8 @@
 /*
  * cgal_helper.h - Conversions between poly2d and CGAL
  *
- * Written 2012 by Werner Almesberger
- * Copyright 2012 by Werner Almesberger
+ * Written 2012, 2015 by Werner Almesberger
+ * Copyright 2012, 2015 by Werner Almesberger
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -21,6 +21,8 @@
  */
 
 extern "C" {
+	#include <stdbool.h>
+
 	#include "poly2d.h"
 }
 
@@ -35,7 +37,7 @@ typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
 typedef CGAL::Polygon_2<K> Polygon_2;
 
 
-static inline Polygon_2 p2d_to_P2(const struct p2d *p, int ccw)
+static inline Polygon_2 p2d_to_P2(const struct p2d *p, bool ccw)
 {
 	const struct v2d *v;
 	Polygon_2 np;
diff --git a/poly2d/p2d_attrib.c b/poly2d/p2d_attrib.c
index 7cde546..48932a2 100644
--- a/poly2d/p2d_attrib.c
+++ b/poly2d/p2d_attrib.c
@@ -1,8 +1,8 @@
 /*
  * p2d_attrib.c - Determine various polygon attributes
  *
- * Written 2012 by Werner Almesberger
- * Copyright 2012 Werner Almesberger
+ * Written 2012, 2015 by Werner Almesberger
+ * Copyright 2012, 2015 Werner Almesberger
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -11,6 +11,7 @@
  */
 
 
+#include <stdbool.h>
 #include <math.h>
 #include <assert.h>
 
@@ -46,7 +47,7 @@ static double angle_3(const struct v2d *a, const struct v2d *b,
  * If we predominantly turn to the right, then the path must be clockwise.
  */
 
-int p2d_is_cw(const struct p2d *p)
+bool p2d_is_cw(const struct p2d *p)
 {
 	const struct v2d *v;
 	double a = 0;
@@ -65,7 +66,7 @@ int p2d_is_cw(const struct p2d *p)
 }
 
 
-int p2d_is_closed(const struct p2d *p)
+bool p2d_is_closed(const struct p2d *p)
 {
 	return p->v == p->last || p->last->next;
 }
@@ -76,7 +77,7 @@ int p2d_is_closed(const struct p2d *p)
  * go unnoticed.
  */
 
-int p2d_no_intersect(const struct p2d *p)
+bool p2d_no_intersect(const struct p2d *p)
 {
 	const struct v2d *v, *u;
 
@@ -106,10 +107,10 @@ int p2d_no_intersect(const struct p2d *p)
 }
 
 
-int p2d_vertices(const struct p2d *p)
+unsigned p2d_vertices(const struct p2d *p)
 {
 	const struct v2d *v;
-	int n = 0;
+	unsigned n = 0;
 
 	v = p->v;
 	while (v) {
diff --git a/poly2d/poly2d.h b/poly2d/poly2d.h
index 407994f..023ec51 100644
--- a/poly2d/poly2d.h
+++ b/poly2d/poly2d.h
@@ -121,10 +121,10 @@ struct p2d *p2d_reverse(const struct p2d *p);
  * p2d_vertices counts the number of vertices in a polygon.
  */
 
-int p2d_is_cw(const struct p2d *p);
-int p2d_is_closed(const struct p2d *p);
-int p2d_no_intersect(const struct p2d *p);
-int p2d_vertices(const struct p2d *p);
+bool p2d_is_cw(const struct p2d *p);
+bool p2d_is_closed(const struct p2d *p);
+bool p2d_no_intersect(const struct p2d *p);
+unsigned p2d_vertices(const struct p2d *p);
 
 /*
  * Convert a possibly self-intersecting polygon into one or more simple