diff --git a/changelog.d/fixes/9633-npm-build-files.md b/changelog.d/fixes/9633-npm-build-files.md
new file mode 100644
index 0000000000..c1dc5128da
--- /dev/null
+++ b/changelog.d/fixes/9633-npm-build-files.md
@@ -0,0 +1 @@
+- fix(build): add build-next-isolated.mjs sibling imports to package.json files array
diff --git a/package.json b/package.json
index ba0b667569..b1430ec223 100644
--- a/package.json
+++ b/package.json
@@ -34,8 +34,11 @@
     "scripts/dev/tls-options.mjs",
     "scripts/check/check-supported-node-runtime.ts",
     "scripts/dev/sync-env.mjs",
-    "scripts/build/native-binary-compat.mjs",
+    "scripts/build/assembleStandalone.mjs",
+    "scripts/build/backendOnlyPages.mjs",
     "scripts/build/build-next-isolated.mjs",
+    "scripts/build/build-tproxy-native.mjs",
+    "scripts/build/native-binary-compat.mjs",
     "scripts/build/runtime-env.mjs",
     "README.md",
     "LICENSE",
diff --git a/tests/unit/repro-9633.test.ts b/tests/unit/repro-9633.test.ts
new file mode 100644
index 0000000000..7acb750e5a
--- /dev/null
+++ b/tests/unit/repro-9633.test.ts
@@ -0,0 +1,27 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+
+const pkg = JSON.parse(readFileSync("package.json", "utf-8"));
+const files = pkg.files || [];
+
+// #9633: `build-next-isolated.mjs` is published (fixed in #1126), but three of
+// its sibling modules it imports were missing from the `files` whitelist, so
+// `npm run build` on a globally-installed package crashed with ERR_MODULE_NOT_FOUND.
+// The dynamic import of `build-tproxy-native.mjs` (~line 308) and the static
+// imports of `assembleStandalone.mjs` / `backendOnlyPages.mjs` must ship too.
+const NEEDED = [
+  "scripts/build/assembleStandalone.mjs",
+  "scripts/build/backendOnlyPages.mjs",
+  "scripts/build/build-tproxy-native.mjs",
+  "scripts/build/colocateOptionals.mjs",
+];
+
+test("#9633: build-next-isolated.mjs sibling imports present in package.json files[]", () => {
+  for (const needed of NEEDED) {
+    assert.ok(
+      files.some((f) => typeof f === "string" && f === needed),
+      `${needed} is not in package.json files[]`
+    );
+  }
+});