diff --git a/docs/guestfs-hacking.pod b/docs/guestfs-hacking.pod
index c35771732..419a4c29b 100644
--- a/docs/guestfs-hacking.pod
+++ b/docs/guestfs-hacking.pod
@@ -274,8 +274,7 @@ the automake documentation for details.
 
 Runs a subset of the test suite under valgrind.
 
-Any F<Makefile.am> in the tree that has a C<check-valgrind:> target
-will be run by this rule.
+See L</VALGRIND> below.
 
 =item C<make check-valgrind-local-guests>
 
@@ -383,6 +382,35 @@ Do:
 
 =back
 
+=head2 VALGRIND
+
+When you do C<make check-valgrind>, it searches for any F<Makefile.am>
+in the tree that has a C<check-valgrind:> target and runs it.
+
+Writing the F<Makefile.am> and tests correctly to use valgrind and
+working with automake parallel tests is subtle.
+
+If your tests are run via a shell script wrapper, then in the wrapper
+use:
+
+ $VG virt-foo
+
+and in the F<Makefile.am> use:
+
+ check-valgrind:
+     make VG="$(top_builddir)/run @VG@" check
+
+However, if your binaries run directly from the C<TESTS> rule, you
+have to modify the F<Makefile.am> like this:
+
+ LOG_COMPILER = $(VG)
+ 
+ check-valgrind:
+     make VG="@VG@" check
+
+In either case, check that the right program is being tested by
+examining the F<tmp/valgrind*> log files carefully.
+
 =head1 SUBMITTING PATCHES
 
 Submit patches to the mailing list:
diff --git a/run.in b/run.in
index ed4109c80..c91183416 100755
--- a/run.in
+++ b/run.in
@@ -33,13 +33,10 @@
 #
 # The script should also be used for tests like this:
 #
-#   TESTS_ENVIRONMENT = ... $(top_builddir)/run --test [$(VG)]
+#   TESTS_ENVIRONMENT = ... $(top_builddir)/run --test
 #
 # The --test parameter introduces a timeout, stopping tests from
 # running forever.
-#
-# Use the optional $(VG) when the tests must also be run under
-# valgrind.
 
 #----------------------------------------------------------------------