diff --git a/MagickCore/effect.c b/MagickCore/effect.c
index 87bbb19..48a2adf 100644
--- a/MagickCore/effect.c
+++ b/MagickCore/effect.c
@@ -2943,7 +2943,7 @@
         gamma=0.0;
         pixel=0.0;
         if ((GetPixelChannelTraits(image,AlphaChannel) == UndefinedPixelTrait) ||
-            (channel == AlphaChannel))
+            (channel == AlphaPixelChannel))
           {
             for (j=0; j < (ssize_t) n; j+=(ssize_t) step)
             {