diff --git a/libvips/resample/shrinkv.c b/libvips/resample/shrinkv.c
index 4743706fe..8badcaef0 100644
--- a/libvips/resample/shrinkv.c
+++ b/libvips/resample/shrinkv.c
@@ -400,7 +400,7 @@ vips_shrinkv_uchar_vector_gen(VipsRegion *out_region,
 		s.left = r->left;
 		s.top = (r->top + y) * shrink->vshrink;
 		s.width = r->width;
-		s.height = chunk_height * shrink->vshrink;
+		s.height = chunk_height * shrink->vshrink + 1;
 #ifdef DEBUG
 		printf("vips_shrinkv_uchar_vector_gen: requesting %d lines from %d\n",
 			s.height, s.top);