--- rpl/Makefile.am	2013/03/04 09:48:19	1.63
+++ rpl/Makefile.am	2013/03/05 23:05:42	1.64
@@ -12,7 +12,7 @@ EXTRA_DIST = LIMITATIONS Licence_CeCILL_
 		rplcas/@COCOA@.tar.gz rplcas/@PARI@.tar.gz rplcas/@GIAC@.tar.gz
 
 all:
-	@if [ -n $(shell $(MAKE) -v | grep "^GNU Make") ]; then \
+	@if [ x$(shell $(MAKE) -v | grep "^GNU Make") != x ]; then \
 		echo; \
 		echo MAKE=$(MAKE); \
 		echo "Please use GNU Make !"; \