-$define|true|[yY]*) d_Gconvert='sprintf((b),"%.*Lg",(n),(x))' ;;
+$define|true|[yY]*)
+ case "`/usr/sbin/sizer -v`" in
+ *[1-4].0*) cat >&4 <<EOF
+
+***
+*** Sorry, you cannot use long doubles in pre-V5.0 releases of Tru64.
+***
+
+Cannot continue, aborting.
+
+EOF
+ exit 1
+ ;;
+ esac
+ d_Gconvert='sprintf((b),"%.*Lg",(n),(x))'
+ ;;