diff --git a/pipi/filter/color.c b/pipi/filter/color.c
index bbc191b..b241ff4 100644
--- a/pipi/filter/color.c
+++ b/pipi/filter/color.c
@@ -155,7 +155,7 @@ pipi_image_t *pipi_contrast(pipi_image_t *src, double val)
                     dstdata[d + 1] = p < 0. ? 0. : p > 1. ? 1. : p;
                     p = (srcdata[d + 2] - 0.5) * val + 0.5;
                     dstdata[d + 2] = p < 0. ? 0. : p > 1. ? 1. : p;
-                    p = (srcdata[d + 3] - 0.5) * val + 0.5;
+                    p = srcdata[d + 3];
                     dstdata[d + 3] = p;
                 }
             }