diff --git a/pipi/dither/ordered.c b/pipi/dither/ordered.c
index f91a722..8c4bede 100644
--- a/pipi/dither/ordered.c
+++ b/pipi/dither/ordered.c
@@ -29,7 +29,7 @@ pipi_image_t *pipi_dither_halftone(pipi_image_t *img, double r, double angle)
 {
 #define PRECISION 4.
     pipi_image_t *ret, *kernel;
-    int k = (r * PRECISION / sqrt(2.) + .5);
+    int k = (r * PRECISION / 2. / sqrt(2.) + .5);
 
     kernel = pipi_render_halftone(k, k);
     ret = pipi_dither_ordered_ext(img, kernel, 1. / PRECISION, angle + 45.);