diff --git a/changelog.d/9481-9249-strict-mode-store.md b/changelog.d/9481-9249-strict-mode-store.md
new file mode 100644
index 0000000000..da6be8d5f5
--- /dev/null
+++ b/changelog.d/9481-9249-strict-mode-store.md
@@ -0,0 +1,16 @@
+**test(9249): opt the blocked-store case into strict mode (#9426 semantics)**
+
+`reflect_define_property_non_writable_prototype_index_blocks_array_store`
+asserted a `TypeError` from a sloppy-mode script. #9426 made a rejected
+array-element write throw **only in strict mode** — which matches node:
+
+| | output |
+|---|---|
+| Perry, with `"use strict"` | `TypeError 1 P` |
+| Perry, as written (script) | `no error 1 P` |
+| `node --experimental-strip-types`, same `.ts` | `no error 1 P` |
+
+Perry and node agree exactly, so the code is right and the expectation was
+stale. The test's purpose — a non-writable inherited index BLOCKS the store —
+is still worth keeping, so it opts into strict mode rather than weakening the
+assertion to the sloppy no-op.
diff --git a/crates/perry/tests/issue_9249_array_prototype_define_property.rs b/crates/perry/tests/issue_9249_array_prototype_define_property.rs
index 7abc78182f..9aa254290d 100644
--- a/crates/perry/tests/issue_9249_array_prototype_define_property.rs
+++ b/crates/perry/tests/issue_9249_array_prototype_define_property.rs
@@ -111,7 +111,15 @@ console.log(hits, values.length, values[5]);
 #[test]
 fn reflect_define_property_non_writable_prototype_index_blocks_array_store() {
     compile_and_run(
-        r#"
+        r#""use strict";
+// #9426 made a rejected array-element write throw ONLY in strict mode, which
+// is what node does. This file is a bare .ts — the oracle
+// (`node --experimental-strip-types`) runs it as a SCRIPT, i.e. sloppy, where
+// the rejected store silently no-ops in node too:
+//   $ node --experimental-strip-types <this program without "use strict">
+//   no error 1 P
+// The point of this test is that a non-writable inherited index BLOCKS the
+// store, so it opts into strict mode rather than asserting the sloppy no-op.
 Reflect.defineProperty(Array.prototype, 11, {
   value: "P",
   writable: false,