diff --git a/automotive/evs/aidl/android/hardware/automotive/evs/EvsEventDesc.aidl b/automotive/evs/aidl/android/hardware/automotive/evs/EvsEventDesc.aidl
index ebff98f..3abdb54 100644
--- a/automotive/evs/aidl/android/hardware/automotive/evs/EvsEventDesc.aidl
+++ b/automotive/evs/aidl/android/hardware/automotive/evs/EvsEventDesc.aidl
@@ -33,7 +33,9 @@
     @utf8InCpp
     String deviceId;
     /**
-     * Possible additional vendor information that is opaque to the EvsManager
+     * Possible additional vendor information that is opaque to the EvsManager.
+     * The size of the payload must not exceed 16-byte if the HIDL recipients are
+     * expected to exist.
      */
     int[] payload;
 }
diff --git a/automotive/evs/aidl/android/hardware/automotive/evs/IEvsCameraStream.aidl b/automotive/evs/aidl/android/hardware/automotive/evs/IEvsCameraStream.aidl
index 2c2b44c..c599d58 100644
--- a/automotive/evs/aidl/android/hardware/automotive/evs/IEvsCameraStream.aidl
+++ b/automotive/evs/aidl/android/hardware/automotive/evs/IEvsCameraStream.aidl
@@ -47,7 +47,10 @@
     /**
      * Receives calls from the HAL each time an event happens.
      *
-     * @param in event EVS event with possible event information.
+     * @param in event EVS event with possible event information.  If ths HIDL
+     *                 recipients are expected to exist, the size of the event
+     *                 payload must not exceed 16 bytes; otherwise, a notification
+     *                 will not reach them.
      */
     void notify(in EvsEventDesc event);
 }