diff --git a/compel/plugins/std/string.c b/compel/plugins/std/string.c
index bde1bc68b..d67e0d1a9 100644
--- a/compel/plugins/std/string.c
+++ b/compel/plugins/std/string.c
@@ -151,7 +151,12 @@ static unsigned int __conv_val(unsigned char c)
 	if (__isdigit(c))
 		return c - '0';
 	else if (__isalpha(c))
-		return &conv_tab[__tolower(c)] - conv_tab;
+		/**
+		 * If we want the value of something which __isalpha() == true
+		 * it has to be base > 10. 'A' = 10, 'B' = 11 ... 'Z' = 35
+		 */
+		return __tolower(c) - 'a' + 10;
+
 	return -1u;
 }