diff --git a/21-Timing.inc.md b/21-Timing.inc.md
index 1a96dcf..e421ff1 100644
--- a/21-Timing.inc.md
+++ b/21-Timing.inc.md
@@ -398,7 +398,7 @@ The [=availability window=] is calculated as follows:
1. Let now be the current wall clock time according to the [=wall clock=].
1. Let AvailabilityWindowStart be now - MPD@timeShiftBufferDepth
.
* If `MPD@timeShiftBufferDepth` is not defined, let AvailabilityWindowStart be the [=effective availability start time=].
-1. Let TotalAvailabilityTimeOffset be the sum of all `@availabilityTimeOffset` values that apply to the adaptation set (those directly on the `AdaptationSet` element and any of its ancestors).
+1. Let TotalAvailabilityTimeOffset be the sum of all `@availabilityTimeOffset` values that apply to the adaptation set, either via `SegmentBase`, `SegmentTemplate` or `BaseURL` elements ([[!MPEGDASH]] 5.3.9.5.3).
1. The [=availability window=] is the time span from AvailabilityWindowStart to now + TotalAvailabilityTimeOffset
.