diff --git a/codex-cli/src/text-buffer.ts b/codex-cli/src/text-buffer.ts
index fe4e2a47..150feec9 100644
--- a/codex-cli/src/text-buffer.ts
+++ b/codex-cli/src/text-buffer.ts
@@ -34,6 +34,10 @@ function clamp(v: number, min: number, max: number): number {
  * ---------------------------------------------------------------------- */
 
 function toCodePoints(str: string): Array<string> {
+  if (typeof Intl !== "undefined" && "Segmenter" in Intl) {
+    const seg = new Intl.Segmenter();
+    return [...seg.segment(str)].map((seg) => seg.segment);
+  }
   // [...str] or Array.from both iterate by UTF‑32 code point, handling
   // surrogate pairs correctly.
   return Array.from(str);