diff --git a/spec/mainadditions.html b/spec/mainadditions.html
index 6d28b4a6ef..fd566195cd 100644
--- a/spec/mainadditions.html
+++ b/spec/mainadditions.html
@@ -283,7 +283,7 @@
SystemTimeZoneIdentifier ( ): a String
1. If the implementation only supports the UTC time zone, return *"UTC"*.
- 1. [declared="s"] Let _systemTimeZoneString_ be the String representing the host environment's current time zone, either: a primary time zone identifier; or an offset time zone identifier.
+ 1. [declared="s"] Let _systemTimeZoneString_ be the String representing the host environment's current time zone, either: a primary time zone identifier; or an offset time zone identifier String _s_ for which ParseText(StringToCodePoints(_s_), |NormalizedUTCOffset|) returns a Parse Node.
1. If IsTimeZoneOffsetString(_systemTimeZoneString_) is *true*, return _systemTimeZoneString_.
1. Return _systemTimeZoneString_.