diff --git a/src/base/ftlcdfil.c b/src/base/ftlcdfil.c
index d12f75337..f40bbeae5 100644
--- a/src/base/ftlcdfil.c
+++ b/src/base/ftlcdfil.c
@@ -272,6 +272,8 @@
   {
     static const FT_Byte  light_filter[5] =
                             { 0, 85, 86, 85, 0 };
+    /* the values here sum up to a value larger than 256, */
+    /* providing a cheap gamma correction                 */
     static const FT_Byte  default_filter[5] =
                             { 0x10, 0x40, 0x70, 0x40, 0x10 };