diff --git a/include/sys/zfs_ioctl.h b/include/sys/zfs_ioctl.h
index c8a02aa66..91439d4b7 100644
--- a/include/sys/zfs_ioctl.h
+++ b/include/sys/zfs_ioctl.h
@@ -124,6 +124,13 @@ typedef enum drr_headertype {
  * default use of "zfs send" won't encounter the bug mentioned above.
  */
 #define	DMU_BACKUP_FEATURE_SWITCH_TO_LARGE_BLOCKS (1 << 27)
+/* flag #28 is reserved for a Nutanix feature */
+/*
+ * flag #29 is the last unused bit. It is reserved to indicate a to-be-designed
+ * extension to the stream format which will accomodate more feature flags.
+ * If you need to add another feature flag, please reach out to the OpenZFS
+ * community, e.g., on GitHub or Slack.
+ */
 
 /*
  * Mask of all supported backup features