--- a/src/testdir/Makefile
+++ b/src/testdir/Makefile
@@ -4,9 +4,11 @@
 
 VIMPROG = ../vim
 
-# Uncomment this line for using valgrind.
-# The output goes into a file "valgrind.$PID" (sorry, no test number).
-# VALGRIND = valgrind --tool=memcheck --leak-check=yes --num-callers=15 --logfile=valgrind
+# Uncomment this line to use valgrind for memory leaks and extra warnings.
+#   The output goes into a file "valgrind.testN"
+#   Vim should be compiled with EXITFREE to avoid false warnings.
+#   This will make testing about 10 times as slow.
+# VALGRIND = valgrind --tool=memcheck --leak-check=yes --num-callers=15 --log-file=valgrind.$*
 
 SCRIPTS = test1.out test2.out test3.out test4.out test5.out test6.out \
 		test7.out test8.out test9.out test10.out test11.out \