Index: /issm/trunk-jpl/m4/issm_options.m4
===================================================================
--- /issm/trunk-jpl/m4/issm_options.m4	(revision 15664)
+++ /issm/trunk-jpl/m4/issm_options.m4	(revision 15665)
@@ -528,25 +528,30 @@
 	AC_ARG_WITH([gsl-dir],
 	  AS_HELP_STRING([--with-gsl-dir=DIR], [gsl root directory.]),
-	  [GSL_ROOT=$withval],[GSL_ROOT=""]) 
+	  [GSL_ROOT=$withval],[GSL_ROOT="no"]) 
+
 	AC_MSG_CHECKING(for gsl)
 	
-	if test -d "$GSL_ROOT"; then
-
-		dnl defaults
-		HAVE_GSL=yes
-		GSLINCL="-I$GSL_ROOT/include"
-
-		if test "x$HAVE_ATLAS" = "xyes" ; then
-			GSLLIB="-dy -L$GSL_ROOT/lib -lgsl -L$ATLAS_ROOT/lib -lcblas -latlas -lm"
+	if test "x$GSL_ROOT" = "xno" ; then
+		HAVE_GSL=no
+	else
+		if test -d "$GSL_ROOT"; then
+
+			dnl defaults
+			HAVE_GSL=yes
+			GSLINCL="-I$GSL_ROOT/include"
+
+			if test "x$HAVE_ATLAS" = "xyes" ; then
+				GSLLIB="-dy -L$GSL_ROOT/lib -lgsl -L$ATLAS_ROOT/lib -lcblas -latlas -lm"
+			else
+				GSLLIB="-dy -L$GSL_ROOT/lib -lgsl -lgslcblas -lm"
+			fi
+
+			AC_DEFINE([_HAVE_GSL_],[1],[with gsl in ISSM src])
+			AC_SUBST([GSLINCL])
+			AC_SUBST([GSLLIB])
+
 		else
-			GSLLIB="-dy -L$GSL_ROOT/lib -lgsl -lgslcblas -lm"
-		fi
-
-		AC_DEFINE([_HAVE_GSL_],[1],[with gsl in ISSM src])
-		AC_SUBST([GSLINCL])
-		AC_SUBST([GSLLIB])
-
-	else
-	AC_MSG_ERROR([gsl directory provided ($GSL_ROOT) does not exist]);
+			AC_MSG_ERROR([gsl directory provided ($GSL_ROOT) does not exist]);
+		fi
 	fi
 	AM_CONDITIONAL([GSL], [test x$HAVE_GSL = xyes])