diff --git a/gr-sim/fire/fire.c b/gr-sim/fire/fire.c
index f92fb4cf..c5b5e3cd 100644
--- a/gr-sim/fire/fire.c
+++ b/gr-sim/fire/fire.c
@@ -1,3 +1,5 @@
+/* Note, based on info from http://fabiensanglard.net/doom_fire_psx/ */
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>