diff --git a/hicolor.h b/hicolor.h
index 76959dc..41e3678 100644
--- a/hicolor.h
+++ b/hicolor.h
@@ -337,6 +337,7 @@ hicolor_result hicolor_write_header(
 }
 
 /* "a dither" is a public-domain dithering algorithm by Øyvind Kolås.
+ * This function implements pattern 3.
  * https://pippin.gimp.org/a_dither/ */
 uint8_t hicolor_a_dither_channel(
     uint8_t intensity,
@@ -347,7 +348,7 @@ uint8_t hicolor_a_dither_channel(
 {
     double mask = (double) ((x + y * 237) * 119 & 255) / 255.0;
     double normalized = (double) intensity / 255.0;
-    double dithered_normalized = floor(levels * normalized + mask) / levels;
+    double dithered_normalized = fmin(1.0, floor(levels * normalized + mask) / levels);
     return (uint8_t) (dithered_normalized * 255);
 }