diff --git a/targettest/c64/pet2scrcode.s b/targettest/c64/pet2scrcode.s
index 870814a94..e20893b2f 100644
--- a/targettest/c64/pet2scrcode.s
+++ b/targettest/c64/pet2scrcode.s
@@ -1,3 +1,6 @@
+    ; Taken from https://codebase64.org/doku.php?id=base:petscii_to_screencode&s[]=petscii, by Mace
+
+
     .export _petscii2scrcode