Index: /issm/trunk-jpl/m4/issm_options.m4
===================================================================
--- /issm/trunk-jpl/m4/issm_options.m4	(revision 15660)
+++ /issm/trunk-jpl/m4/issm_options.m4	(revision 15661)
@@ -548,5 +548,5 @@
 
 	else
-		HAVE_GSL=no
+	AC_MSG_ERROR([gsl directory provided ($GSL_ROOT) does not exist]);
 	fi
 	AM_CONDITIONAL([GSL], [test x$HAVE_GSL = xyes])