diff --git a/src/mux/anim_encode.c b/src/mux/anim_encode.c
index 31bd0457..deeb414a 100644
--- a/src/mux/anim_encode.c
+++ b/src/mux/anim_encode.c
@@ -191,7 +191,8 @@ int WebPAnimEncoderOptionsInitInternal(WebPAnimEncoderOptions* enc_options,
   return 1;
 }
 
-// This starting value is more fit to WebPCleanupTransparentAreaLossless().
+// This value is used to match a later call to WebPReplaceTransparentPixels(),
+// making it a no-op for lossless (see WebPEncode()).
 #define TRANSPARENT_COLOR   0x00000000
 
 static void ClearRectangle(WebPPicture* const picture,