diff -Naur profil-old/bias/biasf.c profil-new/bias/biasf.c
--- profil-old/bias/biasf.c	1996-03-15 13:29:26.000000000 +0100
+++ profil-new/bias/biasf.c	2005-10-19 14:20:59.000000000 +0200
@@ -337,15 +337,16 @@
    */
 {
   REAL x_inf, x_sup;
+  REAL y_inf, y_sup;
 
   x_inf = BiasInf (pX); x_sup = BiasSup (pX);
   if ((x_inf < -1.0) || (x_sup > 1.0))
     _BiasError ("ArcCos argument out of range");
-  x_inf = asin (x_inf);
-  x_sup = asin (x_sup);
-  x_inf = RoundDown (x_inf);
-  x_sup = RoundUp   (x_sup);
-  BiasHullRR (pR, & x_inf, & x_sup);
+  y_inf = acos (x_sup);
+  y_sup = acos (x_inf);
+  y_inf = RoundDown (y_inf);
+  y_sup = RoundUp   (y_sup);
+  BiasHullRR (pR, & y_inf, & y_sup);
 }
 
 VOID BiasArcTan (const PBIASINTERVAL pR, const PBIASINTERVAL pX)