diff --git a/std/assembly/util/string.ts b/std/assembly/util/string.ts
index 6eed06e09f..0ae05927dc 100644
--- a/std/assembly/util/string.ts
+++ b/std/assembly/util/string.ts
@@ -551,7 +551,7 @@ export function isCaseIgnorable(c: u32): bool {
 
 // @ts-ignore: decorator
 @inline
-export function isFinalSigma(buffer: usize, index: i32, len: i32): bool {
+export function isFinalSigma(buffer: usize, index: isize, len: isize): bool {
   const lookaheadLimit = 30; // max lookahead limit
   var found = false;
   var pos = index;
@@ -565,15 +565,15 @@ export function isFinalSigma(buffer: usize, index: i32, len: i32): bool {
         return false;
       }
     }
-    pos -= i32(c >= 0x10000) + 1;
+    pos -= isize(c >= 0x10000) + 1;
   }
   if (!found) return false;
   pos = index + 1;
   var maxPos = min(pos + lookaheadLimit, len);
   while (pos < maxPos) {
-    let c = <u32>load<u16>(buffer + (<usize>pos << 1));
+    let c = <u32>load<u16>(buffer + (pos << 1));
     if (u32((c & 0xFC00) == 0xD800) & u32(pos + 1 != len)) {
-      let c1 = <u32>load<u16>(buffer + (<usize>pos << 1), 2);
+      let c1 = <u32>load<u16>(buffer + (pos << 1), 2);
       if ((c1 & 0xFC00) == 0xDC00) {
         c = (c - 0xD800 << 10) + (c1 - 0xDC00) + 0x10000;
       }
@@ -581,18 +581,18 @@ export function isFinalSigma(buffer: usize, index: i32, len: i32): bool {
     if (!isCaseIgnorable(c)) {
       return !isCased(c);
     }
-    pos += i32(c >= 0x10000) + 1;
+    pos += isize(c >= 0x10000) + 1;
   }
   return true;
 }
 
 // @ts-ignore: decorator
 @inline
-function codePointBefore(buffer: usize, index: i32): i32 {
+function codePointBefore(buffer: usize, index: isize): i32 {
   if (index <= 0) return -1;
-  var c = <u32>load<u16>(buffer + (<usize>index - 1 << 1));
+  var c = <u32>load<u16>(buffer + (index - 1 << 1));
   if (u32((c & 0xFC00) == 0xDC00) & u32(index - 2 >= 0)) {
-    let c1 = <u32>load<u16>(buffer + (<usize>index - 2 << 1));
+    let c1 = <u32>load<u16>(buffer + (index - 2 << 1));
     if ((c1 & 0xFC00) == 0xD800) {
       return ((c1 & 0x3FF) << 10) + (c & 0x3FF) + 0x10000;
     }