diff --git a/tools/test.py b/tools/test.py
index 39e1d827c2853f..e457075a1c5395 100755
--- a/tools/test.py
+++ b/tools/test.py
@@ -1238,6 +1238,9 @@ def ClassifyTests(self, cases, env):
       outcomes = reduce(set.union, outcomes_list, set())
       unused_rules.difference_update(matches)
       case.outcomes = set(outcomes) or set([PASS])
+      # slow tests may also just pass.
+      if SLOW in case.outcomes:
+        case.outcomes.add(PASS)
       result.append(case)
     return result, unused_rules