diff --git a/src/Lib/Polygon/polygon.cxx b/src/Lib/Polygon/polygon.cxx
index 58be765e..84931e9d 100644
--- a/src/Lib/Polygon/polygon.cxx
+++ b/src/Lib/Polygon/polygon.cxx
@@ -132,7 +132,7 @@ void TGPolygon::set_elevations( double elev ) {
 
 
 // Calculate theta of angle (a, b, c)
-static double calc_angle(point2d a, point2d b, point2d c) {
+double tgPolygonCalcAngle(point2d a, point2d b, point2d c) {
     point2d u, v;
     double udist, vdist, uv_dot, tmp;
 
@@ -213,7 +213,7 @@ double TGPolygon::minangle_contour( const int contour ) {
 	p3.x = c[p3_index].x();
 	p3.y = c[p3_index].y();
 
-	angle = calc_angle( p1, p2, p3 );
+	angle = tgPolygonCalcAngle( p1, p2, p3 );
 
 	if ( angle < min_angle ) {
 	    min_angle = angle;
diff --git a/src/Lib/Polygon/polygon.hxx b/src/Lib/Polygon/polygon.hxx
index 6a7c728a..62c5a169 100644
--- a/src/Lib/Polygon/polygon.hxx
+++ b/src/Lib/Polygon/polygon.hxx
@@ -37,6 +37,8 @@
 #include STL_STRING
 #include <vector>
 
+#include "point2d.hxx"
+
 SG_USING_STD(ostream);
 SG_USING_STD(string);
 SG_USING_STD(vector);
@@ -192,6 +194,10 @@ typedef poly_list::iterator poly_list_iterator;
 typedef poly_list::const_iterator const_poly_list_iterator;
 
 
+// Calculate theta of angle (a, b, c)
+double tgPolygonCalcAngle(point2d a, point2d b, point2d c);
+
+
 // canonify the polygon winding, outer contour must be anti-clockwise,
 // all inner contours must be clockwise.
 TGPolygon tgPolygonCanonify( const TGPolygon& in_poly );