diff --git a/src/core.js b/src/core.js
index 1c4f9cb..a02d35d 100644
--- a/src/core.js
+++ b/src/core.js
@@ -67,7 +67,7 @@ export function findUnicodeRangeIndex(cp, ranges) {
   let lo = 0
     , hi = ranges.length - 1;
   while (lo <= hi) {
-    let mid = lo + hi >>> 1
+    const mid = lo + hi >>> 1
       , range = ranges[mid];
     if (cp < range[0]) hi = mid - 1;
     else if (cp > range[1]) lo = mid + 1;
diff --git a/src/grapheme.js b/src/grapheme.js
index 256337f..c066a4f 100644
--- a/src/grapheme.js
+++ b/src/grapheme.js
@@ -52,7 +52,7 @@ export function* graphemeSegments(input) {
   let cursor = 0;
 
   /** @type {number} Total length of the input string. */
-  let len = input.length;
+  const len = input.length;
 
   /** @type {GraphemeCategoryNum | null} Category of codepoint immediately preceding cursor, if known. */
   let catBefore = null;
@@ -64,7 +64,7 @@ export function* graphemeSegments(input) {
   let catBegin = null;
 
   /** @type {import('./_grapheme_data.js').GraphemeCategoryRange} */
-  let cache = [0, 0, 2 /* GC_Control */];
+  const cache = [0, 0, 2 /* GC_Control */];
 
   /** @type {number} The number of RIS codepoints preceding `cursor`. */
   let risCount = 0;
@@ -232,11 +232,11 @@ function cat(cp, cache) {
     // If this char isn't within the cached range, update the cache to the
     // range that includes it.
     if (cp < cache[0] || cp > cache[1]) {
-      let index = findUnicodeRangeIndex(cp, grapheme_ranges);
+      const index = findUnicodeRangeIndex(cp, grapheme_ranges);
       if (index < 0) {
         return 0;
       }
-      let range = grapheme_ranges[index];
+      const range = grapheme_ranges[index];
       cache[0] = range[0];
       cache[1] = range[1];
       cache[2] = range[2];