$OpenBSD$
--- simgear/scene/sky/cloud.cxx.orig	Sat Jul  6 14:13:13 2013
+++ simgear/scene/sky/cloud.cxx	Sat Jul  6 14:14:02 2013
@@ -736,7 +736,7 @@ 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 ( std::isnan(course) ) {
                 course = last_course;
             } else {
                 last_course = course;