diff --git a/simgear/scene/sky/cloud.cxx b/simgear/scene/sky/cloud.cxx
index e62384b9..d4557064 100644
--- a/simgear/scene/sky/cloud.cxx
+++ b/simgear/scene/sky/cloud.cxx
@@ -46,7 +46,7 @@ inline int (isnan)(double r) { return isnan(r); }
 #endif
 
 #if defined (__FreeBSD__)
-inline int isnan(double r) { return !(r < 0 || r > 0); }
+inline int isnan(double r) { return !(r <= 0 || r >= 0); }
 #endif