diff --git a/libavcodec/faanidct.c b/libavcodec/faanidct.c
index f7bea3e083..3844a7b416 100644
--- a/libavcodec/faanidct.c
+++ b/libavcodec/faanidct.c
@@ -20,6 +20,7 @@
  */
 #include "mpegvideo.h"
 
+/* To allow switching to double. */
 #define FLOAT float
 
 #define B0 1.0000000000000000000000