diff --git a/src/gnome-shell.in b/src/gnome-shell.in
index 772a8cf6f..2dfb4f3a0 100644
--- a/src/gnome-shell.in
+++ b/src/gnome-shell.in
@@ -439,7 +439,7 @@ def run_performance_test():
         # version here for simplicity. Using json.dump(indent=0) doesn't real
         # improve the readability of the output much.
         report = {
-            'date': datetime.datetime.now().isoformat(),
+            'date': datetime.datetime.utcnow().isoformat() + 'Z',
             'events': events,
             'monitors': monitors,
             'metrics': metric_summaries,