diff --git a/src/decoder_internal.h b/src/decoder_internal.h
index 9e7e2037a..2347fdf4e 100644
--- a/src/decoder_internal.h
+++ b/src/decoder_internal.h
@@ -36,6 +36,11 @@ struct decoder {
 	 */
 	double timestamp;
 
+	/**
+	 * This flag is set by decoder_seek_where(), and checked by
+	 * decoder_command_finished().  It is used to clean up after
+	 * seeking.
+	 */
 	bool seeking;
 
 	/**