diff --git a/spa/include/spa/node/io.h b/spa/include/spa/node/io.h
index 810a3997d..c1fad81e8 100644
--- a/spa/include/spa/node/io.h
+++ b/spa/include/spa/node/io.h
@@ -122,6 +122,7 @@ struct spa_io_position_video {
 struct spa_io_position {
 	struct spa_io_clock clock;		/**< clock position of driver, always valid and
 						  *  read only */
+	uint32_t size;				/**< size of current cycle expressed in clock.rate */
 	struct spa_fraction rate;		/**< overal rate of the graph */
 #define SPA_IO_POSITION_FLAG_BAR	(1<<0)
 #define SPA_IO_POSITION_FLAG_VIDEO	(1<<1)