diff --git a/libvips/mosaicing/mosaic.c b/libvips/mosaicing/mosaic.c
index 11e1aade..b14bef9f 100644
--- a/libvips/mosaicing/mosaic.c
+++ b/libvips/mosaicing/mosaic.c
@@ -2,6 +2,8 @@
  *
  * 22/5/14
  * 	- from vips_mosaic()
+ * 4/9/18
+ * 	- add docs for transform output
  */
 
 /*
@@ -329,6 +331,12 @@ vips_mosaic_init( VipsMosaic *mosaic )
  * * @hwindow: %gint, half window size
  * * @harea: %gint, half search size 
  * * @mblend: %gint, maximum blend size
+ * * @dx0: %gint, output, detected displacement
+ * * @dy0: %gint, output, detected displacement
+ * * @scale1: %gdouble, output, detected first order scale
+ * * @angle1: %gdouble, output, detected first order rotation
+ * * @dx1: %gdouble, output, detected first order displacement
+ * * @dy1: %gdouble, output, detected first order displacement
  *
  * This operation joins two images left-right (with @ref on the left) or
  * top-bottom (with @ref above) given an approximate overlap.
@@ -346,6 +354,9 @@ vips_mosaic_init( VipsMosaic *mosaic )
  * The detected displacement is used with vips_merge() to join the two images
  * together. 
  *
+ * You can read out the detected transform with @dx0, @dy0, @scale1, @angle1,
+ * @dx1, @dy1.
+ *
  * See also: vips_merge(), vips_insert().
  *
  * Returns: 0 on success, -1 on error