diff --git a/index.bs b/index.bs
index bdbe6df..4f81200 100644
--- a/index.bs
+++ b/index.bs
@@ -1122,9 +1122,10 @@ with the internal slots described in the following table:
     The {{Sensor/timestamp}} getter steps are:
 
     1. Let |global| be [=this=]'s [=relevant global object=].
-    2. Let |unsafeTimestamp| be the result of invoking [=get value from latest reading=] with
+    1. Let |unsafeTimestamp| be the result of invoking [=get value from latest reading=] with
        [=this=] and "timestamp" as arguments.
-    3. Return [=relative high resolution time=] with |unsafeTimestamp| and |global|.
+    1. If |unsafeTimestamp| is null, return null.
+    1. Otherwise, return [=relative high resolution time=] with |unsafeTimestamp| and |global|.
 </div>
 
 ### Sensor.start() ### {#sensor-start}