$OpenBSD$
--- simgear/scene/sky/cloud.cxx.orig	Tue Mar  2 18:14:25 2010
+++ simgear/scene/sky/cloud.cxx	Tue Mar  2 18:15:04 2010
@@ -695,7 +695,7 @@ bool SGCloudLayer::reposition( const SGVec3f& p, const
         // this happens, lets just use the last known good course.
         // This is a hack, and it would probably be better to make
         // calc_gc_course_dist() more robust.
-        if ( isnan(course) ) {
+        if ( __isnanf(course) ) {
             course = last_course;
         } else {
             last_course = course;