diff --git a/ablescript/src/base_55.rs b/ablescript/src/base_55.rs
index a822227..3cabcb1 100644
--- a/ablescript/src/base_55.rs
+++ b/ablescript/src/base_55.rs
@@ -1,4 +1,4 @@
-pub fn char2num(character: char) -> i32 {
+pub fn char2num(character: char) -> isize {
     match character {
         'Z' => -26,
         'Y' => -25,
@@ -66,7 +66,7 @@ mod tests {
     use super::*;
     #[test]
     fn str_to_base55() {
-        let chrs: Vec<i32> = "AbleScript".chars().map(char2num).collect();
+        let chrs: Vec<isize> = "AbleScript".chars().map(char2num).collect();
         assert_eq!(chrs, &[-1, 2, 12, 5, -19, 3, 18, 9, 16, 20]);
     }
 }