diff --git a/qapi/block-core.json b/qapi/block-core.json
index 76bf50f..dd763dc 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -2065,6 +2065,12 @@
 # BLOCK_JOB_CANCELLED event.  Before that happens the job is still visible when
 # enumerated using query-block-jobs.
 #
+# Note that if you issue 'block-job-cancel' after 'drive-mirror' has indicated
+# (via the event BLOCK_JOB_READY) that the source and destination are
+# synchronized, then the event triggered by this command changes to
+# BLOCK_JOB_COMPLETED, to indicate that the mirroring has ended and the
+# destination now has a point-in-time copy tied to the time of the cancellation.
+#
 # For streaming, the image file retains its backing file unless the streaming
 # operation happens to complete just as it is being cancelled.  A new streaming
 # operation can be started at a later time to finish copying all data from the