diff --git a/twasm/asm/main.asm b/twasm/asm/main.asm
index b570cf2..1402364 100644
--- a/twasm/asm/main.asm
+++ b/twasm/asm/main.asm
@@ -68,7 +68,7 @@ copy_token:
 ; rsi -> word to be written
 ;
 ; returned:
-; rax = byte that was read
+; al = byte that was read; the rest of rax is zeroed
 ; ------------------------------------------------------------------------------
 
 copy_byte: