diff --git a/tests/scripts/run-metatests.sh b/tests/scripts/run-metatests.sh
index 182bf04..09a6f8a 100755
--- a/tests/scripts/run-metatests.sh
+++ b/tests/scripts/run-metatests.sh
@@ -6,6 +6,14 @@
 Run all the metatests whose platform matches any of the given PLATFORM.
 A PLATFORM can contain shell wildcards.
 
+Expected output: a lot of scary-looking error messages, since each
+metatest is expected to report a failure. The final line should be
+"Ran N metatests, all good."
+
+If something goes wrong: the final line should be
+"Ran N metatests, X unexpected successes". Look for "Unexpected success"
+in the logs above.
+
   -l  List the available metatests, don't run them.
 EOF
 }