diff --git a/poly2d/p2d_contains_point.c b/poly2d/p2d_contains_point.c
index d6bd8a3..1a1f24d 100644
--- a/poly2d/p2d_contains_point.c
+++ b/poly2d/p2d_contains_point.c
@@ -34,13 +34,15 @@
  */
 
 
+#include <stdbool.h>
+
 #include "poly2d.h"
 
 
-int p2d_contains_point(const struct p2d *p, const struct v2d *v)
+bool p2d_contains_point(const struct p2d *p, const struct v2d *v)
 {
 	const struct v2d *j, *i;
-	int in = 0;
+	bool in = 0;
 
 	j = p->v;
 	do {
diff --git a/poly2d/poly2d.h b/poly2d/poly2d.h
index 023ec51..9cc8e9e 100644
--- a/poly2d/poly2d.h
+++ b/poly2d/poly2d.h
@@ -1,8 +1,8 @@
 /*
  * poly2d.h - The public face of the 2D Polygon library
  *
- * Written 2012, 2013 by Werner Almesberger
- * Copyright 2012, 2013 Werner Almesberger
+ * Written 2012, 2013, 2015 by Werner Almesberger
+ * Copyright 2012, 2013, 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
@@ -147,7 +147,7 @@ void p2d_free_all(struct p2d *p);
  * Returns non-zero if the point is inside or on the simple polygon.
  */
 
-int p2d_contains_point(const struct p2d *p, const struct v2d *v);
+bool p2d_contains_point(const struct p2d *p, const struct v2d *v);
 
 /*
  * Returns: