diff --git a/libvips/conversion/sequential.c b/libvips/conversion/sequential.c
index f9e392c1..5ab04cc0 100644
--- a/libvips/conversion/sequential.c
+++ b/libvips/conversion/sequential.c
@@ -71,7 +71,7 @@
 #include "pconversion.h"
 
 /* Stall threads that run ahead for up to this long, in seconds. Normally they
- * will be woken up long before this, once their data is ready. The timeout is
+ * will be woken once their data is ready and long before this. The timeout is
  * just to prevent a total crash in the case of accidental deadlock. 
  *
  * This has to be a long time: if we're trying to use all cores on a busy 
diff --git a/tools/vipsthumbnail.c b/tools/vipsthumbnail.c
index cb250fc2..a946bc0e 100644
--- a/tools/vipsthumbnail.c
+++ b/tools/vipsthumbnail.c
@@ -490,7 +490,7 @@ thumbnail_shrink( VipsObject *process, VipsImage *in,
 	if( vips_tilecache( in, &t[4], 
 		"tile_width", in->Xsize,
 		"tile_height", 10,
-		"max_tiles", (nlines * 2) / 10,
+		"max_tiles", 1 + (nlines * 2) / 10,
 		"access", VIPS_ACCESS_SEQUENTIAL,
 		"threaded", TRUE, 
 		NULL ) )