diff --git a/api.bs b/api.bs
index 5443bb9..ccf1d4d 100644
--- a/api.bs
+++ b/api.bs
@@ -1248,7 +1248,8 @@ The <dfn method for=PrivateAttribution>saveImpression(|options|)</dfn> method st
         the [=user agent=]'s upper limit.
     1.  If the [=list/size=] of
         |options|.{{PrivateAttributionImpressionOptions/conversionSites}} is
-        greater than an [=implementation-defined=] maximum value, throw a {{RangeError}}.
+        greater than an [=implementation-defined=] maximum value, return
+        [=a promise rejected with=] a {{RangeError}} in |realm|.
     1.  Let |conversionSites| be the [=set=] that is the result
         of invoking [=parse a site=]
         for each value in |options|.{{PrivateAttributionImpressionOptions/conversionSites}}.