diff --git a/payloads/libpayload/libc/string.c b/payloads/libpayload/libc/string.c
index ce5767e4b0..cc587c82a2 100644
--- a/payloads/libpayload/libc/string.c
+++ b/payloads/libpayload/libc/string.c
@@ -407,7 +407,7 @@ static int _offset(char ch, int base)
         if (ch >= '0' && ch <= '9')
                 return ch - '0';
         else
-                return tolower(ch) - 'a';
+                return 10 + tolower(ch) - 'a';
 }
 
 /**