--- a/alphabet.cpp	2023-04-14 21:35:23.646820868 +0530
+++ b/alphabet.cpp	2023-04-14 22:09:01.836357064 +0530
@@ -400,7 +400,7 @@
 
 const char *iupacs = "!ACMGRSVTWYHKDBN!acmgrsvtwyhkdbn";
 
-char mask2iupac[16] = {
+signed char mask2iupac[16] = {
 	-1,
 	'A', // 0001
 	'C', // 0010