diff --git a/index.bs b/index.bs
index c24fe3cc1f..cca8a715b9 100644
--- a/index.bs
+++ b/index.bs
@@ -1673,7 +1673,7 @@ To <dfn noexport>parse source-registration JSON</dfn> given a [=byte sequence=]
 1. Let |maxAttributionsPerSource| be the result of running
     [=parse an optional 64-bit signed integer=] with |value|, "`max_event_level_reports`", and
     [=default event-level attributions per source=][|sourceType|].
-If |maxAttributionsPerSource| is greater than 20, return null.
+1. If |maxAttributionsPerSource| is greater than 20, return null.
 1. Let |eventReportWindow| be the result of running [=parse an expiry=] with
     |value|, "`event_report_window`", and |expiry|.
 1. If |eventReportWindow| is an error, return null.