diff --git a/libvips/conversion/insert.c b/libvips/conversion/insert.c
index 324ab0d2..5f07aff0 100644
--- a/libvips/conversion/insert.c
+++ b/libvips/conversion/insert.c
@@ -504,8 +504,6 @@ vips_insert_class_init( VipsInsertClass *class )
 		_( "insert image @sub into @main at @x, @y" );
 	vobject_class->build = vips_insert_build;
 
-	/* Can't be UNBUFFERED, we are a SMALLTILE operation.
-	 */
 	operation_class->flags = VIPS_OPERATION_SEQUENTIAL;
 
 	VIPS_ARG_IMAGE( class, "main", 0, 
diff --git a/libvips/mosaicing/merge.c b/libvips/mosaicing/merge.c
index b083c7da..d003deab 100644
--- a/libvips/mosaicing/merge.c
+++ b/libvips/mosaicing/merge.c
@@ -2,6 +2,8 @@
  *
  * 22/5/14
  * 	- from vips_merge()
+ * 13/6/17
+ * 	- tag as SEQUENTIAL
  */
 
 /*
@@ -97,6 +99,7 @@ vips_merge_class_init( VipsMergeClass *class )
 {
 	GObjectClass *gobject_class = G_OBJECT_CLASS( class );
 	VipsObjectClass *object_class = (VipsObjectClass *) class;
+	VipsOperationClass *operation_class = VIPS_OPERATION_CLASS( class );
 
 	gobject_class->set_property = vips_object_set_property;
 	gobject_class->get_property = vips_object_get_property;
@@ -105,6 +108,8 @@ vips_merge_class_init( VipsMergeClass *class )
 	object_class->description = _( "merge two images" );
 	object_class->build = vips_merge_build;
 
+	operation_class->flags = VIPS_OPERATION_SEQUENTIAL;
+
 	VIPS_ARG_IMAGE( class, "ref", 1, 
 		_( "Reference" ), 
 		_( "Reference image" ),