diff --git a/quickjs.c b/quickjs.c
index af401ae37..26904fd40 100644
--- a/quickjs.c
+++ b/quickjs.c
@@ -44800,17 +44800,11 @@ static JSValue js_array_sort(JSContext *ctx, JSValueConst this_val,
 
     /* XXX: should special case fast arrays */
     while (n < pos) {
-        if (array[n].str)
-            JS_FreeValue(ctx, JS_MKPTR(JS_TAG_STRING, array[n].str));
-        if (array[n].pos == n) {
-            JS_FreeValue(ctx, array[n].val);
-        } else {
-            if (JS_SetPropertyInt64(ctx, obj, n, array[n].val) < 0) {
-                n++;
-                goto exception;
-            }
-        }
-        n++;
+        i = n++;
+        if (array[i].str)
+            JS_FreeValue(ctx, JS_MKPTR(JS_TAG_STRING, array[i].str));
+        if (JS_SetPropertyInt64(ctx, obj, i, array[i].val) < 0)
+            goto exception;
     }
     js_free(ctx, array);
     for (i = n; undefined_count-- > 0; i++) {
diff --git a/tests/array-sort-write-back.js b/tests/array-sort-write-back.js
new file mode 100644
index 000000000..dba0dc669
--- /dev/null
+++ b/tests/array-sort-write-back.js
@@ -0,0 +1,26 @@
+import { assert, assertThrows } from "./assert.js";
+
+/* Array.prototype.sort writes every sorted value back with Set(..., true),
+   even ones that are already in place. */
+
+/* a String's indices are read-only */
+assertThrows(TypeError, () => Array.prototype.sort.call("aa"));
+assertThrows(TypeError, () => Array.prototype.sort.call("ab"));
+
+/* so are a frozen array's, even when it is already sorted */
+assertThrows(TypeError, () => Object.freeze([1, 2]).sort());
+
+/* setters see every write */
+{
+    const writes = [];
+    const o = { length: 2 };
+    for (const i of [0, 1]) {
+        let v = i;
+        Object.defineProperty(o, i, {
+            get: () => v,
+            set: x => { writes.push(i); v = x; },
+        });
+    }
+    Array.prototype.sort.call(o);
+    assert(writes.join(), "0,1");
+}