diff --git a/src/allmydata/web/check_results.py b/src/allmydata/web/check_results.py
index c9c429622..a29ddb188 100644
--- a/src/allmydata/web/check_results.py
+++ b/src/allmydata/web/check_results.py
@@ -583,7 +583,9 @@ class DeepCheckResultsRendererElement(Element, ResultsBase, ReloadMixin):
 
     @renderer
     def runtime(self, req, tag):
-        runtime = time.time() - req.processing_started_timestamp
+        runtime = 'unknown'
+        if hasattr(req, 'processing_started_timestamp'):
+            runtime = time.time() - req.processing_started_timestamp
         return tag("runtime: %s seconds" % runtime)