Index: /issm/trunk-jpl/m4/issm_options.m4
===================================================================
--- /issm/trunk-jpl/m4/issm_options.m4	(revision 24875)
+++ /issm/trunk-jpl/m4/issm_options.m4	(revision 24876)
@@ -190,6 +190,17 @@
 		[VENDOR=""]															dnl action if not given
 	)
-	dnl defaults for host OS related variables
-	IS_MAC=no
+
+	AC_MSG_CHECKING([if this is a Mac build])
+	case "${host_os}" in
+		*darwin*)
+			IS_MAC=yes
+		;;
+		*)
+			IS_MAC=no
+		;;
+	esac
+	AM_CONDITIONAL([MAC], [test "${IS_MAC}" == "yes"])
+	AC_MSG_RESULT([${IS_MAC}])
+
 	IS_WINDOWS=no
 	AC_MSG_CHECKING([for vendor compilers])
@@ -285,14 +296,4 @@
 	AC_SUBST([OSLIBS])
 	AC_MSG_RESULT([done])
-
-	AC_MSG_CHECKING([if this is a Mac build])
-	dnl TODO: The following test is a POSIX-compliant way of testing for a
-	dnl		  substring, but is not very readable. Perhaps there is a more
-	dnl		  readable method of achieving the same?
-	if test "${host_os#*\"darwin\"}" == "$host_os"; then
-		IS_MAC=yes
-	fi
-	AM_CONDITIONAL([MAC], [test "${IS_MAC}" == "yes"])
-	AC_MSG_RESULT([${IS_MAC}])
 
 	AC_MSG_CHECKING([if this is a Windows build])