diff --git a/libvips/foreign/dzsave.c b/libvips/foreign/dzsave.c
index aac907e4..f5b9c929 100644
--- a/libvips/foreign/dzsave.c
+++ b/libvips/foreign/dzsave.c
@@ -1923,7 +1923,7 @@ vips_foreign_save_dz_class_init( VipsForeignSaveDzClass *class )
 		_( "Tile overlap in pixels" ),
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
 		G_STRUCT_OFFSET( VipsForeignSaveDz, overlap ),
-		0, 8192, 0 );
+		0, 8192, 1 );
 
 	VIPS_ARG_INT( class, "tile_size", 11, 
 		_( "Tile size" ),